Test Your Pool Chemical IQ

Do you know what you are putting in your pool?

Chemicals are a necessary part of pool maintenance. As much as we would like to eliminate them, it just isn’t practical (or safe) to go without.

However, it is vitally important that you understand what is in the chemicals that you do use, and also when they should be used. Without that understanding, you may be adding many more things than you need to, or in some cases actually doing harm to your clients and/or your pool systems.

Here’s a quick true/false quiz to test your pool chemical IQ.

  1. You should never use “plain” chlorine – instead, use dichlor or trichlor which are specifically made for pools.
  2. You should add a flocculent (blue clarifier) once a week.
  3. Stains on your pool are a sign of metals in the water.
  4. You should shock your pool once a week.
  5. If your water is crystal clear then it’s safe to swim in.



While it’s true that dichlor and trichlor are specifically formulated for pools, it isn’t true that you should always use them. Dichlor and trichlor combine chlorine with cyanuric acid, which acts as a stabilizer. Stabilizer is a must in outdoor pools because sunlight can cause chlorine to dissipate very quickly. However, very little (if any) is needed in indoor pools. Even more important is that chlorine is used up and must be replaced, whereas the stabilizer stays around. So every time you add the dichlor or trichlor to the pool, you’re adding more stabilizer that you probably don’t need. It will build up over time, and it can even reach the point where it interferes with the chlorine’s ability to work. Then things go haywire in a hurry! The only way to remove it is to drain and replace the water.

You can avoid this by not adding stabilizer if you don’t need it. Stabilizer can be purchased separately (it is usually sold as ‘conditioner’), and you can use it with plain chlorine (calcium hypochlorite). Test strips can be used to ensure the proper levels of both the chlorine and the stabilizer.

NOTE: Chlorine in any form should be handled carefully, and always follow directions on the packaging. Do not mix products.


>Flocculants are often referred to as “blue clarifiers”. They are useful when you have cloudy water due to tiny particles that are so small they pass through your filter. The flocculent works by causing these smaller particles to stick together into larger ones. The larger particles can then be trapped in the filter or will fall to the bottom of the pool where they can be vacuumed up.

Flocculants are generally safe to use. They are basically inert polymers – not likely to cause a problem for swimmers or react with other chemicals in the pool. The problem with the statement is “once a week”. If you have adequate filtration and circulation, then adding a clarifier once every two or three weeks is probably sufficient. Don’t assume you need one just because you see cloudy water. After heavy use your water will probably be cloudy for a few hours until your filter has a chance to catch up. When the water is still cloudy after several hours, then a clarifier may be called for.

You need to know that too much flocculent can actually have a reverse effect – it can make your pool cloudier than it was before?

#3 Maybe TRUE, maybe FALSE

Stains on the side of your pool MIGHT be caused by metals. However, they might also be caused by algae or other organics.

It seems logical that a rust colored stain is a sign of iron in your water, so you might purchase a product designed to remove it. However, most metal removers add phosphates to the water, and algae LOVE phosphates. If your stain is actually algae, then using the metal remover will cause the algae to multiply rapidly, making things MUCH worse.

The key here is to determine what is really causing the problem before you try to treat it. First, try a little pH reducer on the stain by putting the powder in an old sock and placing it on the stain for a few minutes. The acid in the pH reducer will remove metal stains, but will have little or no effect on algae. Alternatively, try a little laundry bleach or pool chlorine, which should remove algae but won’t affect metal stains. Better yet – take a water sample to your pool store to be tested for metals.

Once you know the real cause of the problem you can use the proper treatment to correct it.


Yes, you should shock your pool. However, depending on your pool and the use it gets, you might need to shock every day, once a month, or never. There is no magic number to determine how often to shock.

Shocking is a way to remove organics from your water – body oils, perspiration, saliva, skin cells, and all the other goodies that are introduced into the pool when we climb in. If we fail to remove them, then our sanitizers can be rendered ineffective. How often you need to shock is affected by the swimmer load, pool size, and type and level of sanitizer.

To determine when to shock a chlorinated pool, simply measure the free chlorine and total chlorine. When the total is more than 1 ppm greater that the free, shocking is recommended. In a brominated pool, use shock when the bromine levels drop. Add the shock in small increments, since it will cause your bromine levels to rise quickly.


Water that looks good is only one indicator of a well-maintained pool. Clear water could still be way off in pH, which would result in red eyes and skin irritation. Clear water could also have dangerously high levels of chlorine or bromine, excessive bacteria counts, or undesirable nitrates or ammonia.

On the other hand, perfectly safe water might appear cloudy due to small bubbles caused when air is introduced into the pipes, or suspended particles of inert materials.

Your eyes and nose are good starting points for measuring water quality, but they aren’t a guarantee. Water testing is critical. Test strips that measure the critical things (pH, sanitizer level) are inexpensive and easy to use.


Wouldn’t it be nice if we could just have a tablet that we added to the pool once a week that would keep the water clean, clear, and safe? Sadly, it doesn’t exist. What your pool needs is not only different from the pool down the street, it is also different from one day to the next. The best way to keep out of trouble is to be educated. A knowledgeable pool professional is worth their weight in gold. They will test your water (usually for free) and help you find a targeted solution.

In short: Test before you treat, and don’t treat for a problem you don’t have.

Happy swimming!

Answers courtesy of:

The ACWT Pool Guru:
Karen Hunter
22609 102nd Ave SE
Woodinville , WA 98077
425 487-3078