Chlorine Stabilizer for Your Pool

Chlorine stabilizer and cyanuric acid are the same substance. Stabilizer is the marketing name, cyanuric acid is the chemical name, and the bag says one on the front and the other in the ingredients panel. There is one product here, and this page is about buying it without paying twice for it.

What it does, in one sentence: it protects free chlorine from being destroyed by sunlight. How that works and what level to aim for is on the cyanuric acid page.

What is actually in the container

Read the active ingredient line, not the front of the bag. You are looking for cyanuric acid, sometimes written as isocyanuric acid. It is sold three ways.

Granular stabilizer. A white powder or fine crystal, usually the cheapest per pound. This is the default purchase. It dissolves slowly, which matters for how you add it.

Liquid stabilizer or “conditioner.” Cyanuric acid already in solution. It costs more per pound of active ingredient and goes to work faster because the dissolving step is done. Dose from the jug’s own label rather than a granular chart, because concentrations are not standardized across brands.

Inside your chlorine. The one nobody warns you about, and it has its own section below.

Why the store sells it as two different products

Walk the aisle and you will see “chlorine stabilizer” and “pool conditioner” on separate shelves at separate prices. In most cases the active ingredient is identical. Conditioner is the word liquid products tend to use, stabilizer is the word granular products tend to use, and neither means anything chemically. Some shelves carry a “stabilizer and conditioner” bottle, which is one chemical named twice.

Check the ingredient panel before you accept a price difference.

How much you need

HTH publishes the rate and it is easy to work with: 1 lb per 10,000 gallons raises CYA by about 10 ppm. Their own examples run 2 lb for 20 ppm, 3 lb for 30 and 4 lb for 40, per 10,000 gallons.

So the arithmetic is pounds = (gallons ÷ 10,000) × (ppm you want to gain ÷ 10).

The common way this goes wrong is buying against a guessed pool volume. Get the gallons right with the pool volume calculator before you get to the register, because the correction for overshooting is a partial drain. Then buy for the gap you actually have, not a round number of bags. The step-by-step for adding it is on how to raise cyanuric acid level in pool.

The trap: your chlorine may already be adding it

If you use trichlor tablets, you are buying stabilizer whether or not you meant to, and there is no way to turn it off.

Orenda’s figure is the one to remember: “trichlor is only 45.8% chlorine (by weight). The majority of it is cyanuric acid.” So most of every tablet in the floater is stabilizer. The chlorine gets consumed and leaves. The cyanuric acid stays, because Orenda also notes that CYA oxidizes out only over “months and high chlorine levels.”

Dichlor is the other stabilized chlorine and it is also a chlorinated isocyanurate, so it carries cyanuric acid in the same way. I have not found a manufacturer-published figure for how much CYA a pound of dichlor leaves behind, so treat it as something to test around rather than calculate around.

This is why salt pool owners find CYA at 100 ppm without ever buying a bag of stabilizer. The cell goes down in July, tablets keep the pool open for six weeks, and that CYA is still there next spring. If your cell is out of service, the unstabilized options In The Swim recommends for a salt pool are granular cal-hypo at 3 lbs per 10,000 gallons or liquid chlorine at 5 gallons per 10,000. Neither raises CYA.

Do not buy stabilizer and trichlor in the same trip unless you have tested and know you need both.

What the label will and will not tell you

The dosing chart on the bag is reliable. Two things it usually leaves out.

It assumes a chlorine pool. Trouble Free Pool recommends 60 to 90 ppm for a salt water chlorine generator pool against 30 to 60 for a liquid chlorine pool, and Hayward’s manual asks for 60 to 80 ppm with 80 as the target. If you own a salt pool, the label’s target is probably too low. Why is covered on salt water pool stabilizer.

It will not tell you to move your chlorine target with it. The free chlorine level you must hold depends on your CYA level and rises as CYA rises. Raise CYA on Saturday, leave the generator where it was, and you can be under-chlorinated by Wednesday. Set the new target using optimal chlorine levels saltwater pool.

One more from the HTH page: cyanuric acid is mildly acidic, so retest pH and alkalinity after a large dose.

What not to buy

A cyanuric acid reducer. Orenda’s own wording is that “some CYA reducers are on the market, but our customers have told us their results are mixed,” and that nitrifying bacteria products cannot survive in chlorinated water in the first place. Buying one is how people end up doing the drain anyway, a month later. The honest options are on reduce cyanuric acid swimming pool.

More than you need this season. There is no reason to stockpile a chemical that only leaves your pool with the water.

A replacement cell, before you test CYA. A cell is $899 to $1,949 at Leslie’s against a few dollars for a bag of stabilizer. Rule out chemistry first, on salt cell for pool.

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