How to Lower Stabilizer in Swimming Pool Water if Level is too High
Dilution is the Solution
First thing's first here. You can not add chemicals to lower stabilizer. Cyanauric acid (stabilizer) can be added, but in order to lower it, the pool needs to be diluted with fresh water. There is no chemical on the market that you can add to your pool water to lower the stabilizer.
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What is going on with stabilizer?
If the stabilizer level is too high in a pool it will lock the chlorine molecules rendering them ineffective as a sanitizer. This usually happens as a result of using chlorine tablets which contain cyanauric acid. Pools that sanitize the water using salt systems or other methods other than tablets usually don't have this problem. Although you will get a chlorine reading, sometimes a high chlorine reading, yet your pool has algae or other problems. This is because the chlorine molecules are nearly useless because they have been locked up from the high cyanuaric acid level.
What level should the stabilzer be?
Between 30 and 50ppm. Test the stabilizer or have your water tested and see what the stabilizer level is. (some pool stores list it as either stabilizer or cyanauric acid level) I service some commercial pools and the county health inspectors like it below 100ppm which makes sense because the chlorine is usually very controllable and effective below this level. Ideally though between 30 and 50ppm.
Diluting the pool water
Depending on your stabilizer level, and of course the size of your pool, unfortunately you are going to have to drain a significant amount of water from the pool. Some customers I have don't like this because of the cost of replacing the water. If you DON'T do this though, you will have recurring problems. If you have a cartridge filter, you may want to check this out. Many problems can be caused by a bad filter.
Draining the Water:
Most pool pumps have more than one valve coming to the intake side of the pump. (Skimmer/Main drain) sometimes a third cleaner line. In any case you need to close the skimmer line and open the drain valve on the return side. (If you don't have a drain valve, have one installed! You'll need it anyway) Another option which can be used to drain water from the pool would be a submersible pump in which a garden hose can be used as a drain line.
Drain about 2 feet of water from the pool. (yes, 18-24 inches below the bottom of the tile line) This is why the skimmer line needs to be closed. Reset the valves and add water from the hose. This can take several hours depending on the size of the pool and water pressure from your hose. Let the pool filter on normal cycle and have the stabilizer re-tested. There should be a significant decrease in stabilizer.
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Questions & Answers
Do you add the stabilizer chemical to the pool or the water return?
You will add the stabilizer directly into the skimmer. Stabilizer does not dissolve quickly, so it's not a good idea to put it directly into the pool; however, it will gradually dissolve when added through the skimmer.