Bob Lowry Explains Trichlor Tablets and Pool Acid Cautions
Pool chemistry rewards careful thinking and punishes assumptions. One of the stickiest myths is that cyanuric acid declines when water evaporates, so trichlor tablets can be used freely in hot, dry climates. Distillation physics says otherwise: evaporation removes pure water only, leaving behind calcium, salts, cyanuric acid, and everything else dissolved. When trichlor adds 10 ppm of free chlorine, it also contributes about 6 ppm of cyanuric acid. At a typical 10 ppm chlorine demand per week, CYA can rise roughly 25 ppm per month and 100 to 150 ppm over a season. That buildup weakens chlorine’s effectiveness and forces partial drains or backwashing to reset levels, because splash-out and leaks are the only real exits for CYA, not evaporation. Every chlorine choice carries a byproduct tradeoff. Trichlor and dichlor add cyanuric acid, liquid chlorine adds salt that becomes part of total dissolved solids, and calcium hypochlorite adds calcium hardness. The question isn’t whether byproduc...