"Chlorine Tabs" Aren't Fully Chlorine — And Your Pool Store Won't Tell You

The pool store's best-selling product is a bucket of chlorine tabs. They call them chlorine tabs. The label says chlorine. The marketing says "keeps your pool clean all week." What they do not tell you is that a chlorine tab is only about 50% chlorine by function. The other 50% is cyanuric acid — a chemical that accumulates in your water permanently, never breaks down, and eventually disables the very chlorine the tabs are supposed to provide.

We wish Frisco pool owners would stop buying chlorine tabs as their primary sanitizer. Here is what is actually inside those tabs, what they do to your pool over time, and what to use instead.

What Is Actually Inside a Chlorine Tab

A standard pool chlorine tab is trichlor — trichloroisocyanuric acid. The chemical formula contains both chlorine and cyanuric acid bonded together. When the tab dissolves in your pool:

• 50-54% becomes available chlorine — this is the sanitizer that kills bacteria and algae
• 46-50% becomes cyanuric acid (CYA) — this stays in the water permanently

Every single tab adds CYA to your pool. Every week, every month, every year. The chlorine portion gets consumed doing its job — killing bacteria, oxidizing contaminants, fighting algae. It gets used up and needs replenishing. The CYA portion does not get consumed. It does not evaporate. It does not get filtered out. It just accumulates.

A pool using 2-3 tabs per week adds approximately 5-10 ppm of CYA per month. After 12 months: 60-120 ppm. After 24 months: 120-240 ppm.

Why CYA Matters (And Why Too Much Is Worse Than None)

CYA is not a bad chemical. At the right level (30-50 ppm), it protects chlorine from UV destruction. The Texas sun destroys unprotected chlorine in 2-3 hours. CYA wraps around chlorine molecules and shields them from UV — extending chlorine's life from hours to days. At 30-50 ppm, this is essential.

The problem starts above 80 ppm. At high concentrations, CYA holds chlorine too tightly. Instead of protecting chlorine while letting it work, high CYA imprisons chlorine. The chlorine is present — your test kit reads 3 ppm — but it cannot release from the CYA to actually kill anything.

At 100+ ppm CYA, your pool is functionally unchlorinated despite testing positive for chlorine. The test reads chlorine because chlorine molecules are in the water. But those molecules are locked up by CYA and cannot sanitize.

This is why pools on tabs eventually go green despite "having chlorine." The homeowner tests, sees 3 ppm free chlorine, and says "my chlorine is fine, why is the pool green?" Because that 3 ppm is bound to CYA and has near-zero killing power.

The Pool Store Incentive

Pool stores sell more chlorine tabs than any other product. A bucket of tabs costs $80-150 and lasts 1-2 months. That is recurring revenue — the customer comes back every month for more tabs. The store knows that tabs cause CYA buildup. They also sell CYA reducers, partial drain services, and "CYA lock breaker" products — all of which exist to fix the problem their primary product created.

The business model: Sell tabs that cause CYA buildup → sell products to fix CYA buildup → sell more tabs that cause CYA buildup again. The customer stays on the treadmill forever.

There is no chemical product that removes CYA from pool water. Any product marketed as a "CYA reducer" either does not work or works so slowly that it is impractical. The only real fix for high CYA is a partial drain and refill — diluting the high-CYA water with fresh water that has zero CYA.

What to Use Instead

Liquid Chlorine (Sodium Hypochlorite)

Contains: 12.5% available chlorine, zero CYA.

This is what every professional pool service uses (or should use). Liquid chlorine adds pure chlorine to the water without any CYA baggage. The chlorine does its job and gets consumed. No CYA accumulation. No chemistry lock. No treadmill.

The tradeoff: Liquid chlorine requires manual dosing at every service visit. You cannot set it and forget it like tabs in a floater. This is why DIY pool owners gravitate toward tabs — tabs are convenient. Liquid chlorine requires effort.

If you maintain your own pool and want to use liquid chlorine: Add 1 gallon of 12.5% liquid chlorine per 15,000 gallons of pool water, 2-3 times per week in summer and 1-2 times per week in winter. Test chlorine before each addition and adjust the dose based on your pool's specific demand.

If you have a pool service: Make sure they use liquid chlorine as the primary sanitizer — not tabs. Ask them. If they drop tabs in your skimmer and leave, your CYA is climbing every week.

Salt Chlorine Generator

Produces: Pure chlorine through electrolysis, zero CYA.

A salt system converts dissolved salt into chlorine gas at the cell plates, which immediately dissolves into hypochlorous acid — the active form of chlorine. No CYA is produced. The system generates chlorine daily, eliminating the need for manual chlorine additions.

You still need some CYA — add it separately as granular stabilizer to reach 30-50 ppm. Then stop. The CYA level stays stable because you are not adding more through tabs. Test quarterly and top up only if it drops below 30 ppm (which happens slowly through splash-out and backwashing).

When Tabs Are Acceptable

Tabs are not evil — they have a role:

Vacation coverage. If you are leaving for 1-2 weeks and nobody is adding liquid chlorine, dropping tabs in the floater maintains a chlorine residual while you are gone. The CYA added over a 2-week period is negligible.

Supplemental between visits. If your pool burns through chlorine faster than weekly service can keep up (heavy use, extreme heat, lots of swimmers), a tab in the skimmer between visits provides supplemental chlorine. Used occasionally, the CYA contribution is minimal.

The rule: Tabs as a supplement — fine. Tabs as your sole sanitizer for months and years — chemistry lock guaranteed.

The Math That Should Convince You

Approach	Annual Chlorine Cost	CYA Added Per Year	Drain Needed?
Tabs only	$600-900	60-120 ppm	Yes, annually ($200-400)
Liquid chlorine only	$400-600	0 ppm	No
Salt system	$0 (electricity only, ~$100/yr)	0 ppm	No
Professional service (liquid chlorine included)	$2,148 ($179/mo)	0 ppm	No

Tabs cost more than liquid chlorine AND require an annual drain to fix the CYA they cause. The "convenient" option is actually the most expensive and most damaging long-term approach.

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Done with the tab treadmill? Hydra Pool Services uses liquid chlorine exclusively — zero CYA buildup, no chemistry lock, no annual drains to fix what tabs broke. All chemicals included in your monthly rate. Start your free 2-week trial →