Key takeaways
- Every trichlor tablet adds both chlorine and cyanuric acid to the water at roughly a 1-to-6 ratio.
- CYA above 80-100 ppm significantly blunts chlorine effectiveness, requiring much higher free chlorine to achieve sanitation.
- Pools that rely on floaters year-round commonly see CYA climb to 150-200 ppm by midsummer without any drain-and-refill.
- Liquid chlorine (sodium hypochlorite) adds no CYA and is often a better primary sanitizer in Austin where stabilizer already accumulates.
- The only reliable way to reduce CYA is partial or full drain and refill; there is no chemical treatment that removes it quickly.
- Weekly professional dosing with liquid chlorine, combined with careful tablet use only as a supplement, keeps CYA in range without constant water changes.
Austin context
Austin & West Austin pools run nearly year-round. A pool that might use 50 tablets in a northern summer can easily consume 150 or more in Austin's long season. Each tablet deposits stabilizer, and Austin's hot, dry summers mean evaporation is high but full drains are infrequent. That combination creates ideal conditions for CYA to accumulate season over season. A pool started fresh in spring with a low stabilizer reading can be at 120-150 ppm by September if the primary sanitizer is trichlor tablets.
Austin fill water does not contain CYA, which means the starting point after a fresh fill or a partial drain resets the clock. But with Austin Water Stage restrictions and drought conditions that sometimes limit non-essential water use, homeowners are understandably reluctant to drain frequently. That makes managing the tablet dose proactively more important than relying on dilution to fix the problem later.
What trichlor tablets actually contain
Trichloro-s-triazinetrione, the chemical name for trichlor, is roughly 90 percent available chlorine by weight. The remaining structure is a cyanurate compound, which means the tablet releases both free chlorine and cyanuric acid as it dissolves. The ratio is approximately 0.6 ppm of CYA added per 1 ppm of free chlorine generated. Some estimates are slightly different depending on the tablet manufacturer, but the direction is always the same: CYA goes up every time a tablet dissolves.
This is by design for outdoor pools. Sunlight degrades chlorine quickly without stabilizer. A modest amount of CYA, around 30-60 ppm for non-saltwater pools, is genuinely helpful and reduces how much chlorine you need to maintain a residual on a bright Austin afternoon. The problem is not that CYA exists in the water; the problem is that it only goes one direction as long as you keep adding trichlor.
- Trichlor tablets: roughly 90 percent available chlorine, remainder is a cyanurate compound.
- Every tablet adds CYA; there is no trichlor tablet that does not.
- Dichlor granules also contain CYA; they are not a workaround.
- Calcium hypochlorite (cal-hypo) adds calcium but no CYA.
- Liquid chlorine (sodium hypochlorite) adds neither CYA nor calcium.
The CYA trap: how it sneaks up on you
When CYA is in the range of 30-60 ppm, it acts as a buffer. It holds chlorine in a reserved state that sunlight cannot break down as quickly. At those levels, the free chlorine your test kit reads is mostly still available to sanitize. As CYA climbs past 80-100 ppm, the chemistry shifts. A larger fraction of the chlorine is locked in a bond with the stabilizer. The number on your test strip still looks like enough chlorine, but the biologically active portion, called hypochlorous acid, is significantly reduced.
This leads to a pattern where owners add more tablets, readings look acceptable, but the pool stays slightly hazy or grows a thin algae bloom that keeps returning after shocking. The shock temporarily spikes chlorine, but CYA suppresses the effective fraction again once the excess burns off. Without addressing the underlying stabilizer level, the pool is in a permanent reactive cycle rather than a steady clean baseline.
- Target CYA: 30-60 ppm for chlorinated pools; 60-80 ppm for saltwater systems.
- At 100 ppm CYA, you need roughly 7.5 ppm free chlorine to match the sanitation of 3 ppm at 50 ppm CYA.
- Test strips often show total chlorine; get a full drop-test or FAS-DPD kit to read free chlorine accurately.
- Clear water does not mean acceptable CYA; test specifically for stabilizer at least monthly.
Floaters: when they help and when to back off
Trichlor floaters are not inherently bad. On pools where CYA is currently low, a single floater can provide a baseline between weekly visits and reduce the amount of liquid chlorine a tech needs to add each service. The issue is treating the floater as the only or primary sanitizer indefinitely. A reasonable approach is to use a floater with a dial that restricts how many tablets dissolve per week, and to pair it with weekly liquid chlorine service that provides the bulk of the sanitizer without adding CYA.
Inline trichlor feeders (the inline erosion-style units often plumbed between the filter and returns) raise the same concern at higher volume. They can be set to a drip rate that rapidly elevates CYA in Austin's warm water, especially if the pool is small or the feeder is loaded heavily. If you have an inline feeder, confirm the feeder rate is conservative and test CYA monthly during high-use months.
- One floater on a 15,000-gallon pool adds less CYA than three; load matters.
- Dial-adjustable floaters let you slow dissolution during rainy weeks when UV is low.
- Remove or close the feeder when CYA approaches 70-80 ppm; switch to liquid for a cycle.
- Do not use a floater as a fire-and-forget solution if you are not testing monthly.
Liquid chlorine as the primary sanitizer
Sodium hypochlorite, the liquid bleach-based chlorine typically sold at 10-12 percent concentration for pool use, is the simplest way to add chlorine without adding CYA. Professional pool services use liquid chlorine almost exclusively as the primary sanitizer for this reason. It allows the tech to dose exactly the right amount based on the test result that day, without any accumulated side effects on stabilizer.
Liquid chlorine does need more frequent addition than tablets because it has no stabilizing carrier. It relies on the CYA already in the water (from initial fills or prior tablet use) to last through daylight. This is why having some CYA in the pool, in the 30-60 ppm range, is still valuable even when using liquid chlorine as the primary sanitizer. The system works well together: a stable moderate CYA level from an initial tablet or two early in the season, then liquid chlorine as the ongoing dose.
When to dilute and how much
If CYA has already climbed above 100 ppm, adding more chemicals will not fix it. The only paths are partial drain and refill, or a full drain. For many Austin pools, a 30 percent drain and refill is enough to bring CYA from 150 ppm down into the 80-100 ppm range, then a second partial drain can bring it further if needed. A full drain gets you back to zero, but that is not always practical or allowed under current water use rules.
Some companies sell so-called CYA reducers or enzyme-based products that claim to lower stabilizer. The evidence base for these products is mixed, and they do not replace dilution for high CYA levels. Ask your pool technician to test the actual CYA level before spending money on chemical treatments; if the number is above 100 ppm, water exchange is the reliable solution.
- 30 percent drain: reduces CYA by roughly 30 percent, same ratio as water replaced.
- 50 percent drain: practical for most pools, requires fill but avoids a full drain.
- Full drain: rarely needed unless CYA is extreme or multiple other chemistry issues exist.
- Check Austin Water restrictions before scheduling any significant drain.
Testing and tracking CYA
Most inexpensive test strip kits include a CYA test, but the strip method is imprecise, particularly at high concentrations. The turbidity-based drop test (where you add reagent and look for a dot to disappear at the bottom of a tube) is more reliable and reasonably easy to use at home. Drop kits are available at most pool supply retailers. Test specifically for CYA at least once a month during the swim season, not just chlorine and pH.
If your weekly service includes a full chemical report, ask whether CYA is on it. A professional service should be tracking stabilizer seasonally and flagging when it is approaching the upper limit. That is part of what you pay for when you have a weekly tech who knows your pool chemistry history.
Common mistakes
- Using a floater loaded with multiple tablets as the only chlorination method, then wondering why algae keeps returning despite normal chlorine readings.
- Testing only chlorine and pH but never checking CYA, so stabilizer creeps to 150+ ppm unnoticed.
- Shocking with trichlor granules or dissolving extra tablets to clear a green pool, which adds more CYA and compounds the problem.
- Assuming clear water means chemistry is balanced; high-CYA pools can look fine while being poorly sanitized.
- Buying enzyme CYA-reducer products without testing CYA first; if the real problem is 180 ppm stabilizer, a partial drain is the only practical fix.
Safe for owners
- Testing free chlorine and CYA monthly with a drop-test kit.
- Adjusting floater dial to slow dissolution when CYA approaches 70 ppm.
- Removing tablets from the floater temporarily when CYA is elevated.
- Adding liquid chlorine as a supplement on a high-UV day between visits.
Call a pro
- Full chemistry panel testing each visit, including CYA and phosphates.
- Determining the right partial drain volume to bring CYA back into range.
- Dosing liquid chlorine accurately based on current test results rather than a fixed tablet schedule.
- Identifying when a floater or inline feeder rate is pushing CYA too fast and adjusting accordingly.
Why weekly care matters
Year-round weekly service is the most reliable way to manage the CYA trap in Austin & West Austin. A weekly tech tests the water before dosing, uses liquid chlorine as the primary sanitizer, and tracks stabilizer trends over time. That approach keeps CYA in range without accumulating the silent buildups that send a pool into a reactive shock cycle every few weeks.
Common questions
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