The Truth About Trichlor Tablets

Trichlor tablets are popular because they dissolve slowly and keep a steady chlorine residual through the week, but they also create confusion that leads to bad pool chemistry decisions. One of the biggest misunderstandings is what cyanuric acid (CYA), also called stabilizer, really does in a swimming pool and what happens when levels get high. CYA does not evaporate, and it tends to build over time when you rely on stabilized chlorine like trichlor. That’s why pool service pros and homeowners can feel like the water “won’t hold chlorine” even though they keep adding more tablets. The episode breaks down these misconceptions so you can protect water quality, avoid algae, and keep sanitizer levels effective without panic or guesswork.

A common story goes like this: someone drains a pool with extremely high CYA, refills it, then tests and still sees a high stabilizer reading. The more realistic explanation is less dramatic: leftover water in plumbing, the filter, or low spots can carry some CYA, and messy cleanup can leave residue that dissolves again once the pool refills. Another key point is testing accuracy. Measuring cyanuric acid above roughly 80 ppm becomes unreliable, and even dilution testing can struggle as the number climbs past 100 ppm. That makes “before and after” comparisons look like CYA is magically surviving a complete drain, when the real issue is often incomplete draining plus limited test precision at very high ranges.

Evaporation creates another myth that keeps CYA problems rolling all season. When water evaporates, only pure water leaves the pool, not dissolved cyanuric acid. So topping off a pool that loses inches to heat and wind does not meaningfully “remove” stabilizer. You may dilute a small amount when you add fresh water, but you are not exporting CYA unless water physically leaves the pool through draining, backwashing, overflow, or splash-out. In hot, dry climates, that constant cycle of evaporate and refill can trick owners into thinking they are managing stabilizer, while trichlor tablets quietly keep adding more CYA week after week.

The core chemistry issue is straightforward: trichlor is not just chlorine. It is trichloroisocyanuric acid, and the product is roughly 50% cyanuric acid by weight. As stabilizer rises, free chlorine becomes less active at any given reading, which means sanitation slows and you need a higher free chlorine target to get the same kill power. The episode cites a practical rule of thumb often discussed in the industry: keep free chlorine around 7.5% of the CYA level. That creates a real-world problem for commercial pools with strict health department limits, because the “needed” free chlorine for high CYA can push the measured reading above what inspectors allow, even if much of that chlorine is effectively buffered by stabilizer.

The good news is that trichlor tablet use can be managed, not feared. You can control cyanuric acid by doing small partial drains during the season, such as taking out several inches and refilling, which physically removes stabilizer and resets water balance. You can also reduce tablet demand by blending in unstabilized chlorine like liquid chlorine (sodium hypochlorite) or cal-hypo during service visits, using tablets more for a residual instead of the entire weekly chlorine plan. The episode also highlights “enhancers” that help chlorine last longer and resist algae, including borates around 50 ppm, mineral systems like PoolRx, and a combined approach of phosphate remover plus enzymes. In rainy regions, natural dilution from heavy seasonal rain can also lower CYA enough that frequent partial drains are less necessary.