Many people I know have had trouble with their swimming pool, and wondered why they spend a lot at the Pool Shop. Instead of explaining some things to some people, this is my attempt to put it all in print. It represents my ideas of how to look after a swimming pool. If you follow this guide, it is at your own risk. I do not guarantee results, nor do I guarantee that everything has a scientific basis. I have to say these things so that no-one will sue me. However I haven't had a complaint, so for all of you who I've talked to, and to anyone who stumbles across this site, this is for you.
Safety is mostly common sense, but please think about these major pool safety problems.
Let's start as if you have just bought a house, it has a pool which is full of something which may have been clean water once, but is now full of leaves and green slime. Where do you start? Before you can do anything, you have to know some basic information. Do not try to clean up the pool until you have found these things out, you may end up with more problems than you started with.
Once you know the size of your pool, you should calculate some basic quantities:
Later on, there is a discussion on various types of chlorine and how they work. If you do not know the benefits and drawbacks of the various types, buy liquid chlorine. It has the least unwanted side effects so you can use it until you decide if it is best for your needs. It will usually be 12% active ingredient or 10% active ingredient. It loses activity with time, don't use material more than 3 months old.
These are the things you should calculate (and write down for future use):
In the following calculations, V is the volume of your pool in '000 (thousands) of litres. E.g. for a 15,000 litre pool, V is 15
If you have a chlorinator, you may need salt. If your chlorinator says it is not making enough chlorine, take a sample of your water (in a thoroughly rinsed 1 litre or larger container) to a pool shop and get it tested. Do not throw in more salt until you have had a test, the chlorinator may be faulty.
The minimum to keep your pool safe for swimming:
I recommend you also have
You could also use a stabiliser (I don't). Before you decide on using a stabiliser, read What is stabiliser?
There are a lot of other things your pool shop will want to sell you. Resist the temptation to buy anything else until you understand what you are doing. Unless you are in an area with 'difficult' water (a lot of dissolved solids) you probably don't need anything more.
As mentioned before, you should have a 4 in 1 test kit (pH, chlorine, total alkalinity, acid demand)
You should also be able to brush the pool surface and vacuum up any solids on the pool floor. If you don't have the tools to do this, get them from a pool supplier. The parts are:
Your pool should look great. If the water is not sparkling clear and the walls of the pool spotless, you should know why. If the water is the least bit cloudy, it should be because you have had a lot of people thrashing about in it, or there's been a big storm, and you will have it back to normal tomorrow. If cloudiness persists, superchlorinate. If cloudiness persists after that, flocculate. After that, you have a problem outside my experience and you should call in an expert. Don't think a sparkling pool is something that requires extra work, it will in fact save you work.
Of course, you will have to empty the skimmer box, clean the filter, adjust the pH and so on as it is required. The saying "a stitch in time saves nine" is very true of pool maintenance, if you skip 5 minutes maintenance for a day or two, it could be a trip to the pool shop on the weekend, and an hour or two of good swimming time wasted. And the pool won't be 'just right' when you want it to be.
It is a good idea to empty the skimmer box every day. Just because the contents are out of sight, doesn't mean they are out of the pool. If there is much in the skimmer box, it can contaminate the water and will slow the water circulation. If your pool gets a lot of debris in it, think of investing in an automatic pool cleaner.
The walls of your pool are sensitive indicators to the quality of the water. If you sight down the wall and it looks the same colour as it does when you look at it from the opposite side of the pool, that's a good indication all is well. If you notice it is a little darker when viewed almost edge on, it is an early sign of contamination. Check your observation by brushing the section of wall. If it lightens up after brushing, you may have an algae problem about to appear, I recommend you correct the pH and increase the chlorine level immediately. It is not necessary to superchlorinate, about two times a sanitary dose should do the trick if the pH is right.
By now, you should have a test kit and supplies, and have calculated the quantities needed to maintain the pool. You should now read The Three Rules which will explain in general terms what you need to do. If the pool is very dirty, there is a section dealing with pool problems, but resist the temptation to jump there directly. I think you should understand a little of what you are doing first. If you decide that you need drastic action, you will also have to read about flocculation. If the pool is a bit green but otherwise OK, you may be able to correct it using normal maintenance.
This section is here just in case you don't know how much water is in your pool. If you have it written down somewhere, skip this section.
You should know how much water is in your pool. It doesn't need to be accurate, within 20% is fine. Most pool makers tell you how much water is needed, or if it is a new pool you can check your water meter before and after filling. If you don't have this information, work it out.
Some pools are a regular shape (round or rectangular) and have level or
constant slope bottoms. These can be worked out by traditional methods:
A rectangular pool volume in litres is (length in metres)*(width in
metres)*(average depth in millimetres)
A circular pool volume in litres is approximately (diameter in
metres)*(diameter in metres)*(average depth in millimetres)*0.8
If the pool is a strange shape you should take the time to work out the volume by the following method. It will take a while but you only need do it once (as long as you don't lose the bit of paper). First, measure the maximum length (L) and width (W) of the pool (in metres, rounding up to the nearest). Lay the tape along the pool edge, and leave a marker at each metre from the start of the tape (a bag of marbles or some pegs will do). Mark up a piece of paper with a grid of squares (W by L), each square will represent one square metre of pool surface. Each square has to be big enough to write three numbers in it. Draw a diagram of the pool on the paper, draw it so the markers (if drawn on the diagram) would be on a line.
Next, work out the average depth of water in each square. For a normal pool which slopes one way this is easy. Working from the shallow end, measure the depth half way between the marbles (in centimetres this time) with a stick, and write it in all the squares on the paper across the pool (it will usually be a number between 50 and 300). If the pool has an odd shaped bottom, you may need a helper, then get in and measure at the centre of each square. Take sightings off the markers to locate which square you are in and get your assistant to write the depth in the appropriate square.
When you have filled in the depth of all the squares, add a second number, 1 to 10, indicating how much pool is in the square. Most squares will be in the pool completely and you write 10, but you will have some squares which are cut by the line representing the edge. This doesn't need to be accurate, it will not make much difference if you put 4, 5 or 6 for a square which is half in the pool and half out. You are likely to make a compensating error on another square and it will even out.
For each square, multiply the first and second number and write it in as the third number. Add up the third number in all the squares and this is the volume of water in litres (phew!).
My three rules of Pool Care are:
There is another guideline:
There is no need to understand what pH is, all you need to know is it should be 7.6 or less. But not less than 7.2. Why is this so? you may ask. Well, it is a compromise between good bacteria killing properties and pool water quality. The killing properties of chlorine are very dependant on pH. You need 4 times as much chlorine at pH 8 as you do at pH 7 to get the same killing effect. But water with pH 7 or below is not nice to swim in, will corrode metal more quickly, eat away grout, and is generally not as pleasant as water of pH 8. Fibreglass pools and pools with plastic liners are more tolerant of acid conditions (lower pH) than concrete pools so in non swimming period it is more acceptable to let the pH go low. Concrete pools should be checked regularly all year round.
You cannot guesstimate pH, so you must test for it. All measuring kits have a pH test. Use it often.
If pH is higher than desired (more than 7.6), add acid. I use Hydrochloric Acid. It should be handled very carefully, do not spill it and avoid breathing the vapour. It is not poisonous but is very unpleasant. If pH is lower than desired (less than 7.2), add an alkaline. My experience is that this is rarely required. My preference is Sodium Bicarbonate, but Sodium Carbonate can be used. Unless you calculate how much material is needed, add small amounts per day (for my 40,000 litre pool I add a maximum of 250ml of acid or 500 grams of Bicarb). If the pH is higher than 7.8, do an 'Acid demand' test and add enough acid to bring it to 7.4.
A common reason pools go green is the pH has risen above 7.6 which means the chlorine is no longer effective
When you measure pH, it is easy to get a false reading. A good technique is to rinse the sample tube in pool water a number of times, then submerge it inverted and draw a sample from some distance under the surface. Add a drop of chlorine neutraliser, rinse the cap in the pool and cap the sample tube, then roll the contents back and forth. Do not shake excessively as this mixes air with the water which can change the reading. Also avoid touching inside the cap or the measuring tube, you can contaminate the sample. Remove the cap, add the required drops of indicator, replace the cap and roll again. As soon as the colour is uniform through the sample, check it against the pH indicator chart. Don't wait, the colour may change and the first stable colour is the most reliable indication. Do not put anything in the sample tube except samples.
It is recommended that you set up a pH buffer in the pool, to prevent the pH changing quickly. This is not necessary for some pool types, but it is highly desirable and can prevent problems immediately after a heavy swim day or a storm. It is cheap insurance, for further information see the section on setting up a pH buffer.
The minimum level of hypochlorous acid (the active component of 'chlorine' chemicals) required for effective killing of undesirable organisms is regarded as 0.6 ppm (parts per million). For a 40,000 litre pool, this is a tiny 24 grams, about the amount in a medicine glass. Unfortunately, the effect of pH is to convert some of the chlorine to an ineffective form (80% effective at pH 7, only 20% effective at pH 8). At pH 7.6, you need at least 1.5 ppm of chlorine (60grams for my pool) to get an effective level of active component. This is why measuring and correcting pH is so important
You can add chlorine as liquid or granular chlorine, and you may have a chlorinator which makes it. The germicidal action of all of the forms is the same, they all end up adding the active compound (hypochlorous acid) to the pool. The difference is what other material is added to the pool, and how much active compound is added. A good way to measure active component is in grams. Some chlorinators have a meter which indicates grams/hour. Liquid chlorine (sodium hypochlorite) is usually 10% or 12% active component, whereas granular chlorine (calcium hypochlorite) is around 65% active. To get a minimum level to ensure my pool is sanitised requires either (1) 4 to 5 hours of chlorinator at 14g/hour, or (2) 600ml of liquid chlorine, or (3) 100gm of granular chlorine. It doesn't matter which is used, the effect is the same.
The amount required per day will vary enormously. In the middle of winter, I find 15 gm/day is sufficient (which can all come from the chlorinator). In summer, I need up to 100gm/day and I 'top up' what the chlorinator makes with liquid chlorine most days. The chlorine is destroyed by UV (ultraviolet) light from the sun, and is used up by chemical reaction with organic material in the pool.
Once you have some experience with your pool, you will be able to guesstimate how much chlorine is needed each day. It will vary with the weather, the season, and how many people swim in it. Until you are confident, use your test kit to test every day during the swimming season, and every three days otherwise. You will probably do this for a year or two until you learn how your pool reacts. After that, test when you feel you need to.
You also need to occasionally superchlorinate your pool, to break down undesirable chemicals. This requires the total level to be raised to 12 ppm or about 8 times the normal level. This level cannot normally be achieved by using a chlorinator, so you need to add chlorine. It is not advisable to swim in the pool the next day.
See what sort of chlorine should I use for a discussion on the pros and cons of each type
Many people use a chlorine stabiliser (Cyanuric Acid or a compound containing cyanurate). This is not necessary, but read the section what is a stabiliser. You may consider your situation can benefit from adding a stabiliser.
The third rule is that there really are only two rules, keep pH right and add enough chlorine. Events will happen which cause one or both of these factors to go out of the desired range. If this happens, especially in warm weather, and you do not act quickly, your pool can go green very quickly. Once algae is established, it reacts with any remaining chlorine in the pool, and very quickly the chlorine level is too low to be effective. In warm weather algae will establish itself in a day and you will have to take special action to get rid of it. It is better to forsee the problem and adjust pH and/or add chlorine before this happens.
The most common events which consume chlorine and upset pH are:
You could run the pool pump and chlorinator while people are in the pool. The level of chlorine after going through the chlorinator is only slightly higher than what is going in, and will not cause a problem. For one or two people, this should compensate for extra chlorine demand and pH should be little changed (especially if you have used a pH buffer).
A simple precautionary measure after a storm or a major pool party is to add enough chlorine to bring the level in the pool from zero to the required level for sanitation. This should be added as soon after the event as is practicable. If there was a storm and it is still raining, take an umbrella and do it, don't wait until morning when the rain has stopped. When the storm is gone, follow this with a pH and chlorine test, to see if further action is needed.
This is a philosophical guideline, but since it is my reason for many recommendations it needs discussion.
What is tolerable in a pool? In general a pool will contain water and salt, maybe some buffer, stabiliser, and flocculant. It will also have the residue from people using the pool and from debris which falls in the pool. Chlorine (hypochlorous acid) will break down most organic debris to simple molecules. Generally, most things will end up as Salt (Sodium, some Potassium, and Chlorine - the element, not a pool chemical), Water (Oxygen and Hydrogen), or one of the gasses in the air (Nitrogen or Carbon Dioxide). We can tolerate and may need a small amount of calcium. Anything else we add should come out again as a solid or a gas. The only other way of getting it out is to pump out the pool and replace the water!
Some of the things worth thinking about are algaecides (often contain dissolved copper), some flocculants (e.g. Alum contains sulphate), and stain removers. Once the chemical is there, how is it removed or broken down. If it breaks down to things that can't be removed, are they safe? some things could accumulate to levels which are undesirable or even toxic to sensitive people. For this reason, I don't use them. This is probably ultra cautious and paranoid, they are all approved as safe by various regulatory bodies.
The chemicals I use break down into the elements hydrogen, carbon, oxygen, chlorine, sodium, potassium, calcium and aluminium. Most organic material breaks down to these elements, and also nitrogen. Apart from Aluminium, all the elements are regarded as absolutely safe as they are present in the body, and mostly at concentrations higher than in pool water. Aluminium is the active component of flocculant, and it is removed from the pool when it is attracted to solids such as dead algae, tiny dirt particles and so on. There is no evidence it is harmful, but I mention it because it is not present in the body in the same concentration.
Of course, before the chemicals break down to their components, they may be a nuisance. But if we know they can be broken down to something safe, the long term safety of the pool is guaranteed.
Most pool books say you cannot over filter a pool, and they are quite right. If money were no object, you would run the pump all the time. But electricity bills and wear and tear on the pump means most people will compromise.
The pump on most pools is sized to pump all the water through the filter in less than 4 hours. But because water swirls around, some water will go through several times and some water will miss out. So it is likely you can't filter all the water in 4 hours. If the water was reasonably clear when you started, it will be clearer when you finish, and may be clear enough to keep you happy. So for you, 4 hours is enough. Other people will want that extra sparkle, and may filter for 10 hours. In summer, 4 hours is probably a minimum unless your pump and filter are unusually large for the pool. In winter, when there are few contaminants, 1 hour a day should be adequate. If you have a chlorinator, you are making 'free' chlorine at the same time.
Don't be fooled by the term 'free' chlorine. In my case, the chlorinator makes 14gm/hour and it costs about 15¢/ hour in electricity to run the pump. However, I buy 25 litre of liquid chlorine for $22, which works out at about 10¢ for 14gm of active chlorine. So it is cheaper to add chlorine than to make it. But as long as the pump is running for some other reason, such as filtering, then the chlorine is effectively free. But don't run the pump just to make chlorine thinking you are saving money. If you are trying to save that last $, it is worth doing all the calulations to see how much it really costs to make chlorine. It is wise to add 2¢/hour for the cost of replacing the chlorinator. This is equivalent to 10,000 hours of use of a $200 chlorinator, about 4 hours a day for 7 years. If you have a small pump, the equation is likely to be more in your favour but rarely is it cost effective with normal pool pumps to make your own chlorine. If you are prepared to make the investment, you could install a separate very small pump just to chlorinate, in which case you may save money in the long term.
To get the best out of the pump and filter, clean the filter regularly. The more pressure it takes to push water through your filter, the less water is circulated. Filter pumps are designed so that you are unlikely to blow up the filter with water pressure. As the pressure builds, the water circulates less and less and if you let the filter clog badly you could be circulating 10% of the full flow, but the electricity bill doesn't go down.
If you have a chlorinator, you can run the pump as many hours as required to create the desired amount of chlorine. In winter this is usually enough, but with larger pools it can get expensive in summer and you can add chlorine as liquid or granular as it is cheaper. You also add either liquid or granular (not slow release) to superchlorinate.
If you have a fibreglass or vinyl lined pool with a chlorinator, I recommend you do not use granular chlorine. It adds unwanted calcium to your pool, and this will deposit on your chlorinator cell, requiring it to be cleaned frequently. Note that many proprietary products contain granular chlorine (e.g. 'Burnout'). You will get the same effect using a larger quantity of liquid chlorine, and it will often cost less than the proprietary product.
If you have a concrete/pebblecrete pool, you should have a small amount of dissolved calcium in your pool to stop the cement/grout dissolving. You will need an advanced test kit which will allow you to determine the calcium level or you should take samples to a pool shop. You will also need to clean your chlorinator regularly. You can use granular chlorine to maintain the calcium level, and liquid chlorine once that level is reached.
Note that pool shops sell bulk calcium hypochlorite (granular chlorine), and also little packets (e.g. 'burnout'). There is no difference between the two, even though you pay much more per Kg for the little packets. If you intend using it, buy it in bulk.
You can also use a cyanurate based chlorine, this is a slow release combination of stabiliser and chlorine. If you need to turn off your pump for an extended period, you can use one of these products so that you don't need to add chlorine every day. If you have a choice on when the pump is turned off, it is recommended that you do this in winter when chlorine demand is lower.
Two calculations are needed:
In Starting Out, these calculations were worked out for liquid chlorine. Here is a more general method which covers the various sorts of chlorine.
First determine what level of chlorine is required to keep the pool sanitised. This should be 1.5 ppm (parts per million) if you don't use stabiliser (cyanuric acid), or 2.5 ppm if you use 40 ppm of stabiliser.
Then calculate the amount of chlorine in grams required to create the
required level
Required grams of chlorine = (volume of pool in '000 litres) * (required level
in ppm)
e.g. for a 50,000 litre unstabilised pool we need 50*1.5 = 75 grams
Now relate this to the method of adding chlorine.
For a chlorinator, hours of running = (grams required)/(chlorinator
rate)
e.g. for a 14gm/hour chlorinator, we need 75/14 = 5-1/2 hours (approx)
For liquid chlorine, look on the container to find the percentage of
active ingredient. This is normally10% or12.5%. It may be expressed as
grams/litre (100gm/litre=10%, 125gm/litre=12.5%). The amount required in ml
(millilitres) is (grams required *100)/(percentage active ingredient).
e.g. for 12.5% active, we need (75*100)/12.5 = 600ml
For granular chlorine, the amount in grams required is approximately
(grams required*3)/2 (one and a half)
e.g. for our example we need 75*3)/2=112.5grams
If ever you are in doubt about the amount of chlorine in the pool (you think it is low), adding this amount will bring it back to a satisfactory level, provided your pH is OK.
The minimum chlorine required to superchlorinate is 12ppm, which is 8 times the amount to keep the pool sanitary when not using stabiliser, or almost 5 times the amount when using stabiliser. You can see with the example pool, you would need to run the chlorinator for 44 hours. But in that time, some chlorine is destroyed by the sun, so it is not practical to superchlorinate this way. You must add chlorine to superchlorinate, either 4.8 litres of liquid or 900gm of granular.
Superchlorination is a completely different process than chlorination. Chlorination is used to kill unwanted organisms in the water and make it safe to swim. Superchlorination is a reaction to break down unwanted chemicals in the pool into simple forms that can be removed or are inactive. It is fortunate that the same hypochlorous chemicals can do both jobs. However, a much higher level is required for superchlorination. After superchlorination the chlorine levels are higher than recommended for pleasant swimming. It could bleach hair and clothing, and may irritate sensitive people. It is not a dangerous level, just a nuisance. It is recommended the pool be left at least a day before it is used again.
The sure indicator that superchlorination is required is that the pool smells of chlorine. This may seem paradoxical as people claim the smell is due to too much chlorine in the water already. This is not true, what you smell is a different compound called chloramine which results from chlorine reacting with organic materials, especially those that contain ammonia compounds. Two of these are perspiration and urine, but suntan oils, facial creams and so on can contribute. Chloramines are water soluble, so accumulate in the pool until they are removed by superchlorination. Chloramine is also an irritant, especially of the eyes. Normal pool water is unlikely to irritate anyone, in a salt water pool it is very close to the same composition as tears.
Be sure that the smell is coming from the pool water, smell it while no-one is in the pool. It is most evident around the inlet jets where the water is stirred up and more likely to release the compound to the air. You could also scoop some water into a container and check it. Don't rely on what you smell when you are in the pool. If the chlorine level is high, your body will give off detectable levels of chloramine while you are in the pool, even though the chloramine level in the pool is low.
Most pool maintainers will superchlorinate according to how much the pool is used, and not wait for detectable levels of chloramine.
You should add Sodium Bicarbonate (Bicarb) to your pool to create a pH buffer. What this means is that the pH will remain more constant when impurities are added to the pool (such as rain, leaves, perspiration). No two pool books seem to agree on just how much is good, however all agree it should be at least 60ppm (parts per million) up to 180 ppm. Fibreglass and lined pools are not affected by the amount of buffer, so lower values (i.e. 60-100ppm) are OK. Pools with grout, such as tiled or concrete pools, need higher values (120-180ppm) to help prevent the pool walls dissolving in the water.
The required amount in grams is approximately (required level in ppm) *
(pool volume '000 litres) * 1.5 grams. Divide by 1000 to get Kg.
e.g. to get 60ppm in a 40,000 litre pool requires 60*40*1.5=3600 grams or 3.6Kg
This is the maximum requirement. If you check the level at regular intervals (and you should aim for at least twice a year), there will be some residual from when you last added Bicarb. To find out how much Bicarb is required, use your test kit to perform a 'Total Alkalinity' test. This tells you the Bicarb level in drops, each drop being 10ppm. If you do this test and the level is more than 25 drops you may have a water problem and you should take a sample to a pool shop for full analysis. Assuming the level is less than the required level, do a calculation of what Bicarb is needed (you should know how to work this out, see Getting Started). Run the pump and add the Bicarb to the pool away from the skimmer box. I add it on the top step. Wait an hour or so and brush any solid residue to break it up. At the same time, add double the sanitary dose of chlorine. This is needed because pH will go alkaline and chlorine is less effective. The Bicarb should all dissolve overnight.
After you add the Bicarb, the pH will rise. You then need to add some acid to bring the pH back to the desired value of 7.2-7.6. Do an 'Acid Demand' test the next day, and calculate much acid to add (you should know how to work this out, see Getting Started). Run the pool pump and add the acid away from the skimmer box. Wait an hour and test the pH. If it is still high, do not immediately add more acid, wait at least another 4 hours. If you are leaving the pool for longer, it is a good idea to add extra chlorine, to ensure the pool remains sanitised. Add a small amount of acid and repeat the process with at least a 4 hour gap between additions until the pH is below 7.6.
If you have a chlorinator, it needs salt in the water to work. The level is
usually 4000 ppm (0.4%) or 7000 ppm (0.7%) depending on the brand of
chlorinator. Look in the chlorinator book, or find out from the manufacturer.
This is a large amount, many 25kg bags in a large pool. Fortunately it is
cheap, but only buy what you need as it is bulky and hard to store.
The total amount in Kg needed is (pool volume in '000 litres * level required
in '000 ppm)
e.g. if you have a 50,000 litre pool and need 0.7% (7000ppm) then you need
50*7=350Kg (or 14 * 25Kg bags)
Salt level should be maintained during the swimming season, but is not so important during winter when the chlorine demand is low. There are no other significant benefits to having salt in the pool, the only purpose is to make chlorine. Add salt at the start of the swimming season, and whenever you think it is needed.
When you add salt, it is a good idea to run the pump for a couple of hours with the chlorinator turned off, to mix the salt in. If you do not turn off the chlorinator, a concentrated patch of salty water may go through the cell, and it could get damaged.
There are several ways to deal with salt level:
Method 1: Take a water sample to a pool shop, let them sell you the salt you need. This is a reasonable option if you can resist the sales pitch to buy other things like algaecide, clarifier, burnout, stabiliser, stain remover, etc. which they might also say you need.
Method 2: If your chlorinator has a needle gauge, you can calculate what you
need by noting the change in the needle when you throw in a known amount (e.g
two bags for a 50,000 litre pool). The gauge should have evenly
spaced graduations to use this method. If it doesn't have them, mark a bit of
paper and stick it on the gauge. It doesn't matter what the scale is, as long
as it is evenly divided.
The amount of salt in the pool (after adding the known amount) is (final
reading * amount added)/(final reading - first reading).
e.g. if the gauge is divided into 20 parts, and the first reading was 8.2 (try
to be this accurate) and the final reading was 9.8 after adding 2 bags (50kg)
then you now have (9.8*50)/(9.8-8.2) = 490/1.6 = approx 306Kg of salt. We
worked out before a 50,000 litre pool should have 350Kg so another 2 bags
should be added to get 7000ppm salt level in the pool. Note that after adding
the extra, the reading should rise to 11.4. This may or may not be "enough"
according to the gauge, even though our calculations say there is now enough
salt. This could be because the chlorinator needs cleaning, the water is cold,
or the chlorinator is near the end of its life. Don't be tempted to throw in
more salt, if you can't work out what the problem is, then get professional
help.
Method 3: Your chlorinator should have an indicator of some sort which will tell you if it is making enough chlorine. Throw salt in until it indicates there is enough. You should do this when the water temperature is above 20C because below that the chlorinator is less effective and you may end up adding more than needed (with the possibility of damaging your expensive chlorinator when the water warms up). This is not a reliable method as it assumes the cell is in good order. But if the indicator is just slightly down and you've had water losses then you would expect to need to replace the lost salt. If the salt level was OK three months before, and you can't bring the reading back to normal by adding 20% of the total salt requirement (for the 50,000 litre pool, that would be three bags), then get the water tested as there may be a problem with the chlorinator.
Sometimes the water will be cloudy even though you know the pH is right, you've killed all the algae with high levels of chlorine, and the filter is clean. This is because some particles are too small to be trapped by the filter, and they continue to circulate in the pool. To get rid of them you need to add a flocculant, which causes the little particles to draw together and form bigger particles which then fall to the bottom.
Unfortunately, the bigger particles are easily broken up, so you should proceed carefully to remove them. Choose a time when the weather is expected to be calm and no rain is expected. I find it best to do the second step (vacuum to waste) in the morning when there is least likelihood of wind.
First, set the pump to bypass the filter (or remove the filter) and turn off the chlorinator. Add water to the pool until the level is 50mm above normal or as full as you can get it if less than 50mm. Then add a superchlorination amount of chlorine, and some flocculant. Unless the pool is really dirty, you can use a lot less flocculant than the amount recommended by the manufacturer. Typically I find a third of the recommended amount is adequate. Let the pump circulate the water for an hour and then turn it off. Disable it so it will not turn on again. Leave the pool at least overnight, preferably 24 hours.
After the pool has been undisturbed, the water should be crystal clear and there will be a layer of floc (fluffy stuff) on the bottom. It is best to have two people for this step, to minimise water usage. Set the pump so it will bypass the filter and vacuum to waste (i.e not back in the pool). Connect the cleaning hose and lower the vacuum head very carefully into the pool, the fluffy layer is extremely delicate and will break up with the slightest agitation. When the head is near the bottom, get your assistant to turn on the pump. Work as smoothly as you can and vacuum up all the fluff. If you cannot reach all the fluff in one series of movement, raise the head from the bottom and get your assistant to turn off the pump until you have carefully moved to the next position. Continue until all the fluff is gone.
If the water level has fallen more than 50mm, you may need to add more. Then set up the pump for normal operation, with the filter in place, and start it. Check the pressure gauge frequently, it may climb very quickly if you missed too much of the fluff. Clean the filter as often as necessary, usually the pressure will settle after one or two cleanings of the filter. Do the usual tests, adjust the pH and add chlorine if needed.
The two forms of chlorine in the pool, hypochlorous acid (the active component) and hypochlorous ion (the inactive component) are both easily broken down by UV radiation from the sun. Most chlorine loss is due to this. Stabiliser (cyanuric acid) 'locks up' some of the chlorine in a form which is not attacked by UV. As the two components are destroyed by the UV, some 'locked' chlorine is released to replace some of the lost material. By this method, chlorine loss is reduced, and so it is unnecessary to add as much.
To achieve good results, the cyanuric acid level should be about 40ppm. Higher levels than this can 'lock up' too much chlorine and leave insufficient levels of active component. Levels higher than 100ppm will lock so much chlorine that it may be necessary to pump out the pool and replace the water. So it is essential to add the right amount. It should be added at least once a year at the start of the swimming season, preferably every three months. Most people do not test for cyanuric acid levels at home (although I believe the kits exist), they take the sample to a pool shop. The test is difficult to interpret and it should be left to someone with experience.
Because some chlorine is 'locked up', the required level is about 1.6 times what you would normally have (i.e. about 2.5 ppm instead of 1.5ppm). That means there is more chlorine in the pool, and since less is broken down by UV, it takes a bigger problem to reduce chlorine levels below effective sanitary levels.
The downside is that you need to keep watch on cyanuric acid levels carefully. If the level falls too far, and you are trying to maintain 2.5 ppm instead of 1.5 ppm, UV will break down more chlorine each day, rather than less. On the other hand, if you have too much cyanuric acid, even 2.5 ppm isn't enough to guarantee a sanitary level of active chlorine.
In a deep pool, the chlorine loss is not as dramatic as in a shallow pool. This is because a deep pool has a larger volume of water (and reserve of chlorine) in relation to its surface area (and exposure to UV rays). A shallow pool in a sunny position will benefit most from a stabiliser, as even quite high levels of chlorine can be depleted by UV to below the sanitary level without stabiliser.
I do not use stabiliser in my pool because experience shows the chlorine reserve is adequate for most occasions, and I try to head off problems before they happen. The cost of extra chlorine is not much more than the cost of cyanuric acid needed to save chlorine use, and I don't have to take my water for testing. But it is a personal preference, many people use stabiliser and are happy with it. If you have a smaller pool, or feel you frequently cannot maintain adequate chlorine levels, then you should consider adding stabiliser.
If your pool is cloudy or has some algae, you have two choices:
There are two problems with aggressive action; (1) it costs more, (2) it takes longer. If you want your pool to look the best for a pool party tomorrow, don't be aggressive or the pool will likely be unusable. Try a minimal approach and even if the pool looks a little off, it will be usable.
If your pool has some algae, looks a bit off colour, and the water is murky, then you may be able to rescue it with minimal action.
This is usually sufficient to recover from minor problems, the chlorine level may be a little high the next day but it will be usable and it will be safe.
For almost all normal problems, a combination of superchlorination and flocculation will solve them. For this it is better to run the pool more alkaline than for the minimal action.
If you are starting with a filthy pool, due to dirt, excess algae, or maybe you have filled it with dam water, or from some other cause, then you have to take drastic action to clean it up. But before you start, consider if you may be overreacting to a situation which can be corrected with normal maintenance. As a guideline, if you put something at the bottom of the pool (say the broom head), and you can see it (even if very fuzzy), then it is possible pH correction and a superchlorination is all that is needed.
First, if there is solid material in the pool, such as dirt or sand, remove as much as you can without using the pump. If you put material like sand or other gritty material through the pump, it will wear the impeller and you may need to replace it. You might be able to sweep dirt and grit to a corner, and if you have a slope away from the pool, syphon the material out. To syphon, fill the vacuum hose with water by immersing it completely, then hold your hand over one end to stop water escaping. Lift the blocked end from the pool and put it down the slope to start the syphon. Before taking your hand off, curl the hose so it runs down the slope and slightly up again. The lowest point should be below the exit so the syphon is not broken by air rushing back up the hose. Take your hand off, and water should flow from the pool through the hose. Suck the dirt out with the end still in the pool.
Do a total alkalinity test on the pool. If the level is below 120ppm (12 drops) calculate how much Sodium Bicarbonate is required to bring it to that level. If it is above 12 drops, continue the test. If more than 25 drops are required, make sure you are doing the test correctly, repeat it being extra careful not to contaminate the sample, and if it still needs more than 25 drops it is best to go to a pool expert to seek advice.
Fill the pool 50mm above the normal level. If the total alkalinity test indicated Sodium Bicarbonate is required, add it now. Add a double superchlorination amount of chlorine. Don't run the pump, stir the pool as best you are able to mix in the chlorine. It is best not to put your hands in the water, use a clean plank or other stirrer, preferably non-metallic. Then add the manufacturer's recommended amount of flocculant and stir the pool manually again. Wait one day for flocculation to occur, then check what solid material is left in the pool once everything is settled. If the water was very dirty to start with, there is likely to be some solid material you have missed, and you might now see it and be able to remove it. This will break up the fluff and dirty the pool again, you will have to wait another few hours for it to settle. Then vacuum to waste.
If you now do an acid demand test, and add the indicated amount of acid, the pool should be close to what you want. If it is still cloudy, you can flocculate it a second time. However, it is probably best to ignore it for a few days, and if it persists after everything else is right, flocculate then. Otherwise, get the pH under control and start your normal maintenance.