How to Add Cyanuric Acid Granules to Pool Water Safely

To add cyanuric acid granules to a pool, turn the pump on and pour the weighed dose slowly into the skimmer, or hang it in a sock in front of a return. Keep the pump running and don’t backwash for 48 hours, then retest. Granules dissolve slowly, so an early test reads low and invites a second dose you can’t take back.

Step by step

It’s ten minutes of work and two days of waiting. The dose (HTH’s rate is 1 lb per 10,000 gallons for 10 ppm) is on how to raise cyanuric acid level.

Weigh a dose sized to real gallons. Check volume with the pool volume calculator, then use a scale, not the scoop.
Clean the filter first. HTH's directions say to clean and backwash before adding, because you can't for two days after.
Add it slowly with the pump on. Into the skimmer a little at a time, or in a sock hung at a return.
Brush off strays. Granules on the floor sit there until you move them.
Run the pump and leave the filter alone for 48 hours. A backwash in that window sends undissolved stabilizer to waste.
Retest CYA, pH and alkalinity at 48 hours. Cyanuric acid is mildly acidic, so a big dose can pull pH down.

Skimmer, sock or broadcast

All three work with the pump running; they differ in where undissolved granules end up.

Skimmer

Fastest

HTH's method. Undissolved granules collect in the basket and filter.

Sock at a return

Cleanest

Granules stay in the bag, out of the filter and off the floor. Squeeze it every few hours.

Broadcast

Brush after

Scatter over the surface, then brush every granule that settles.

The skimmer route is the one HTH prints: “Add the correct dose of this product slowly to the skimmer.” Another brand’s label, Alliance Trading’s Conditioner, says to “Broadcast directly into the pool, scattering over the surface of the water,” and allows the skimmer only “For pools with plastic piping.”

Our pick for salt pools. The sock, because it keeps granules out of the filter and the cell. Whether to switch the cell off meanwhile is on should I turn off the salt cell when adding stabilizer.

Whichever route you use, don’t leave granules on the floor. The Alliance label says to “brush any undissolved product off the pool surface.”

Why you wait 48 hours to retest

HTH says to “Wait 48 hours before retesting” because “CYA dissolves slowly.” Test sooner and part of the dose is still in the sock or the filter.

Timeline from 0 to 48 hours: pump on and no backwash for 48 hours, granules still dissolving for 24 to 48 hours, retest at 48 hours — Using a sock? Start the clock when the bag is empty.

Even at 48 hours, the test can’t see a small step. A paper in The Journal of the Swimming Pool and Spa Industry on the melamine test says: “Monsanto estimates the test precision at 100 mg/L cyanuric acid to be ± 7.5 mg/L.” So a 10 ppm addition can read as no change.

On an 80 to 120 ppm axis, a real 100 ppm reads 92.5 to 107.5 and a real 110 ppm reads 102.5 to 117.5, overlapping between 102.5 and 107.5 — Each bar is the test's plus or minus 7.5 ppm scatter around the true level.

Example. You add 1.5 lb to a 15,000 gallon pool, a 10 ppm step, and the tube reads unchanged. Don’t add another 1.5 lb; retest in a few days before deciding.

Doubling up is expensive because stabilizer barely leaves except with water. Orenda says it “will eventually be oxidized from the water, but it takes months and high chlorine levels,” and concludes that “the most economical way to reduce CYA is to drain and dilute.” The fix is on reduce cyanuric acid swimming pool, and the warning signs are on symptoms of high cyanuric acid in pool.

Frequently asked questions

Can I pour cyanuric acid granules straight into the skimmer?

Yes, slowly and with the pump running, which is HTH’s own method. Check your product’s label first: one brand allows the skimmer only for pools with plastic piping.

Can I just throw stabilizer in the pool?

Some labels say to broadcast it over the surface. Brush any granules that settle until they dissolve.

How long do cyanuric acid granules take to dissolve?

HTH says CYA dissolves slowly and allows 24 to 48 hours of pump circulation before a retest. Swim timing is on how long to wait after adding cyanuric acid.

Should I pre-dissolve the granules in a bucket?

Neither label we checked asks for it: HTH pours into the skimmer and Alliance broadcasts. If you use a bucket anyway, stir until no grit is left, because leftover grit is dose you never added.

What does stabilizer actually do in a salt pool?

It shields chlorine from sunlight. Background and targets are on cyanuric acid for pool, and the rest of running a salt pool is in the salt cell hub.