What’s Inside a Trichlor Tablet? (And Why It Matters)

Trichlor chlorine tablets, often called chlorine pucks, have become one of the most common tools in swimming pool care because they are convenient, potent, and easy to store. They contain roughly 90% available chlorine, which makes them one of the strongest chlorine products by percentage. The catch is that they dissolve slowly, so they are great for steady daily sanitation but a poor choice when a pool is at zero free chlorine or actively growing algae. If you need an immediate chlorine boost for a green pool, liquid chlorine or another fast-acting sanitizer is usually the better move while tablets maintain a baseline. For pool service routes and DIY pool maintenance alike, understanding what trichlor does well and what it cannot do quickly is the first step toward better water quality.

Supply history and pricing also explain why pool owners treat tablets like “the default.” The market shifted over time from older practices like chlorine gas dosing toward stabilized tablet systems, especially as inline chlorinators and floaters became standard. Manufacturing disruptions, including the well-known Biolab factory fire before COVID, helped drive a long-lasting jump in trichlor tablet prices. Even when supply stabilizes, operating costs and production limits tend to keep pricing from returning to old lows. For consumers, that means the real value is not just finding a bucket of pucks, but using them intelligently so you avoid expensive side effects like chronic water replacement, repeated algae treatments, and wasted chemicals from mismanaged chlorine levels.

The most important “hidden” detail is built into the chemistry: trichlor is a stabilized chlorine, and its byproduct is cyanuric acid (CYA), also called pool stabilizer or conditioner. Roughly half the weight of each tablet ultimately becomes cyanuric acid in the water, and you cannot separate that from the product because it is part of the compound itself. Over a season, a heavy tablet user can add a surprising amount of CYA, and cyanuric acid does not evaporate out. High CYA is not automatically a disaster, but it changes the rules of chlorine effectiveness. As CYA rises, a smaller fraction of free chlorine remains active at any moment, so you often need a higher free chlorine target to maintain the same sanitation strength and algae prevention.

That is where practical pool water balance matters. A widely referenced guideline is keeping free chlorine at a minimum of about 7.5% of the cyanuric acid level, so a pool at 100 ppm CYA may need roughly 7.5 to 8 ppm free chlorine to stay reliably effective. Managing CYA typically means partial draining and refilling, dilution from heavy rain in some climates, or reducing tablet dependence by supplementing with liquid chlorine or cal-hypo. Dosing trichlor is also inherently variable because dissolution changes with water temperature, pump run time, floater use versus an inline chlorinator, and the chlorinator dial setting. Finally, handle tablets with care: never place them in the skimmer, secure floaters so they do not sit on steps, and use granular trichlor sparingly to avoid staining or surface burns, especially on vinyl liners and fiberglass pools where low pH exposure can be harsh.