Enter your gallons and the job — get the polyquat 60 dose in ounces, and an honest word on what algaecide can and can't do.
The honest algaecide math
weekly prevention: 3 oz per 10,000 gal
opening / closing: 11 oz per 10,000 gal · visible algae: 15 oz per 10,000 gal
Algaecide is the seatbelt, not the engine. Chlorine at the right level (matched to your stabilizer — the CYA calculator explains that relationship) prevents algae by itself in a well-run pool. The weekly polyquat dose is for the weeks that aren't well-run: the vacation, the heat wave, the forgotten test.
A worked example
A 15,000-gallon pool: 4.5 oz weekly (about half a cup), 16.5 oz at opening, 22.5 oz if algae shows. A quart bottle is 32 oz — seven weeks of prevention for this pool, which is why the quart of polyquat at $25–30 beats the gallon of cheap foamer at the same price.
If your pool is already green
Go to the green pool calculator and run the chlorine process — that's the cure. Algaecide's role in a cleanup is the epilogue: once the water holds chlorine overnight (the overnight test proves it), one preventive dose helps guard the win while the pool finishes clearing.
Frequently asked questions
How much algaecide should I add to my pool?
For polyquat 60 (the type worth buying): about 3 oz per 10,000 gallons weekly for prevention, around 11 oz per 10,000 at spring opening or fall closing, and up to 15 oz per 10,000 when algae is visible. Enter your gallons above for your exact numbers.
Does algaecide actually kill algae?
Honestly: chlorine kills algae; algaecide mostly prevents it. If your pool is already green, the fix is the chlorine process in our green pool calculator — algaecide plays backup there at best. Where algaecide earns its price is insurance: vacation weeks, party weekends, and shoulder seasons when chlorine can slip.
What kind of algaecide should I buy?
Polyquat 60 (polymer, 60% strength) — it doesn't foam and doesn't stain. Cheap 'copper-based' algaecides work but can stain surfaces and turn blond hair green; cheap '10%' quat algaecides foam like a bubble bath. The few extra dollars for polyquat is the rare pool-store upsell that's actually right.
Can I add algaecide and chlorine at the same time?
Add them separately — high chlorine tears up algaecide, wasting both. The clean sequence: shock at night, let chlorine drift back under ~5 ppm, then add algaecide. After a green-pool cleanup, wait until the water holds chlorine overnight before adding the preventive dose.