![]() ![]() Another problem with trichlor tabs is that they are acidic, and most have a pH of about 2.8. The CYA is constantly being added to the water as the trichlor tab dissolves. The main reason I do not recommend using trichlor as the main source of chlorine in residential pool water is that it changes the amount of FC required by the pool daily. This would mean that the FC requirement has gone from 3.75 to 7.5 ppm. ![]() If you started at 50 ppm, it is now 100 ppm. In eight weeks you have added almost 50 ppm more CYA to the pool. Many pools consume about 1 to 1.5 ppm of FC each day, so in a week or 10 days, the CYA will increase by 6 ppm or more if using trichlor. In fact, for trichlor, every 10 ppm of FC added to the water will increase CYA by 6 ppm. Using trichlor or dichlor means that the CYA level will change (and go up) constantly. However, as some of that 3 percent FC that is available gets used to kill and oxidize, some of the bound chlorine replaces the lost FC so that the 3 percent is always available until there is no more chlorine in the water.Īs the CYA level increases it requires a higher FC level to control bacteria and algae. It is not immediately available for disinfection and oxidation. The remaining chlorine in the water (about 97 percent) is bound to CYA. In my article I explained that chlorine in water is mostly bound to the CYA, and only a very small amount of chlorine (about 3 percent) is available to disinfect and oxidize. RELATED: New Thinking: Chlorine/Cyanuric Acid in Balance If you have 2 ppm FC without CYA, you are exposed to all 2.0 ppm FC. So being exposed to even 10 ppm of FC with CYA in the water means that the exposure is only 3 to 7 percent of 10 or 0.3 to 0.7 ppm FC. In addition, CDC and EPA do not consider that chlorine is bound to CYA and that only about 3 to 7 percent of the chlorine is free in the water at any moment. Side note, the CDC’s Model Aquatic Health Code says that you can superchlorinate up to 10 ppm. In fact, EPA says the maximum FC is 4 ppm for swimmers. These are obviously very high levels of FC, and the EPA and CDC say that you should not be exposed to that much chlorine. CYA of 65 ppm would require 5 ppm FC and 100 ppm would need 7.5 ppm FC. The reasoning: 7.5 percent of 50 ppm CYA is 3.75 ppm FC. ![]() In addition, the CYA level needs to be no more than 50 ppm. It's a long article, but here's the most important part: For most residential pools, the FC level should be 7.5 percent of the CYA minimum. I once wrote an article about this subject, which you can read in full here. How much chlorine does a pool need? Why do some pools get algae even with 2-4 ppm free chlorine? I hope I can give you the details so you don't have to figure out what somebody else meant or what you should be doing. Many times I read articles that say, "Maintain this condition at this level," but they fail to tell you how often to do it or how to do it. Now let’s get started with the more complete answers: And because it is acidic, it lowers pH and alkalinity. Using trichlor raises CYA by 6 ppm for each 10 ppm of FC. Using it increases CYA, which requires a higher level of chlorine to kill bacteria and algae. Why is using trichlor as main source of chlorine not a good idea? So the net effect on pH is zero (or almost zero).Ĩ. The amount of HCl is almost identical to the amount of NaOH. But when the HOCl is degraded by UV, and when used in killing and oxidation, it creates HCl (hydrochloric acid). When added to water, liquid chlorine (which has a pH of 13) makes HOCl (hypochlorous acid – the killing form of chlorine) and NaOH (sodium hydroxide), which raises pH. Using liquid chlorine raises the pH of the water. CYA also controls how much free chlorine is available for killing and oxidizing.ħ. CYA only protects chlorine, right? So why should it matter what the level is?ĬYA protects free chlorine from UV destruction, but it also is part of the pH buffering system that keeps the pH from being lowered. ![]()
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