Algaecide Calculator by Strength and Gallons
There is no standard algaecide dose: each bottle's label sets its own, so scale that label to your gallons. At a label dose of 16 fl oz per 10,000 gallons, a 15,000-gallon pool needs 24 fl oz.
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
On this page (9 sections)
Algaecides are sold at many strengths and in several chemical types, and their doses differ a lot from bottle to bottle. Enter the amount and the gallons from your own label, then your pool's gallons; the calculator does the scaling. The example label numbers in the form are placeholders, not a recommended dose. Always follow the product label.
How to scale the dose on your label
Amount for your pool = label amount × your gallons ÷ label gallons. A dose written per 10,000 gallons is multiplied by 1.5 for a 15,000-gallon pool. The calculator also shows the amount per 100 gallons, which helps for small above-ground pools, and converts fluid ounces to milliliters for measuring cups marked in metric.
Measure with a measuring cup, not by "glugs" from the bottle. Too little may not work; too much can make the water foam or turn cloudy.
Why doses differ so much between bottles
Algaecides are EPA-registered pesticides, and each registered label carries its own directions. Two bottles can share a front-label name like "algaecide 60" or "algae control" and still list different amounts, because they differ in active ingredient and concentration. We read five EPA-registered algaecide labels: two 60% polyquats, a 40% quat, a 10% quat, and a copper product. For a newly filled or opened pool, their starting doses ranged from about 6 to about 26 fl oz per 10,000 gallons. Their maintenance doses ranged from about 1.5 to 6.4 fl oz per 10,000 gallons, repeated every 3 to 7 days depending on the label. That is roughly a fourfold spread for the same job. Always follow the product label.
The bottles are not interchangeable. A 10% product is not one-sixth as strong as a 60% product, because the percentages can refer to different active ingredients. Use the label of the bottle in your hand, never a dose from another product or from a website that doesn't name your product.
Initial dose vs maintenance dose
Many labels list two amounts:
- Initial or start-up dose: a larger amount for a newly filled or newly opened pool, or after shocking.
- Maintenance dose: a smaller amount added on a schedule, often weekly.
Enter the line that matches what you are doing. If your label lists a separate amount for visible algae, read its conditions carefully: some labels pair that dose with a chlorine treatment and tell you the order and the chlorine level to keep.
Polyquat, quat, or copper: which type?
| Type | What to look for on the label | Main drawback |
|---|---|---|
| Polyquat | "Poly[oxyethylene(dimethyliminio)ethylene (dimethyliminio)ethylene dichloride]", often sold as "60%" | Costs more per bottle |
| Quat (quaternary ammonium) | "Alkyl dimethyl benzyl ammonium chloride" or similar | Can foam, especially with jets or when overdosed |
| Copper-based | "Copper" or "copper triethanolamine" or similar chelated copper | Can stain surfaces and tint blond hair green |
The labels we read back this up. The 60% polyquat label says the product will not foam. The 40% quat label warns it may foam, while the 10% quat label allows "low foam" claims, so quats vary. The copper label warns that full-strength product will stain porous pool surfaces. In a pool with a vinyl liner or light plaster, or with a history of metal stains, a non-metal algaecide avoids the staining risk. If you already have stains, see pool stains. If your pool foams after a dose, see foamy pool water.
How often to add algaecide
As often as your label says, and only if you need it. Algaecide is a supplement to chlorine, not a replacement: the labels we read still tell you to keep a chlorine or other sanitizer level while you use them. A pool that keeps free chlorine (FC) at or above the minimum for its stabilizer (CYA) level does not grow algae, with or without algaecide. That minimum is on pool chlorine levels.
Weekly maintenance doses make the most sense where chlorine is hard to keep up: pools with heavy sun and debris, pools you can't test often, or the weeks after an algae problem. They are also commonly used when you close the pool for the season. See closing an above-ground pool for the order of shock and algaecide.
Can you add too much algaecide?
Yes. Common signs:
- Foam on the surface, mainly with quat products and running jets or waterfalls.
- Cloudy water that the filter doesn't clear.
- Stains on plaster or liners, or green-tinted hair, with copper products.
Most of these fade as the product breaks down and the filter runs, but copper stays in the water until it is removed or diluted. To prevent this next time, scale the label dose exactly and never add a second dose "to be sure". If you treated algae and it came back, the cause is usually low chlorine, not too little algaecide. To identify the algae, see pool algae types.
Algaecide for an above-ground pool
Use the same label scaling. Small pools need small doses, so measure carefully: the per-100-gallons line in the calculator helps. Check that the label allows use in vinyl-lined or above-ground pools, and be cautious with copper products on light liners. Pool sizes for common models are on the above-ground pool gallons chart.
Safety
Never mix algaecide with chlorine or any other chemical in a bucket or a feeder. Add it directly to the pool with the pump running, separately from other products. Wear gloves and eye protection. Keep swimmers out for the time on the label. Store it sealed and out of children's reach. Poison Control: 1-800-222-1222. Always follow the product label. It is a violation of federal law to use a pesticide product in a manner inconsistent with its labeling.
FAQ
Is 60% algaecide better than 10%?
Not necessarily. The percentages often refer to different active ingredients, so they don't compare directly. Compare the type, the label dose, and the price per treatment for your pool, not the percent on the front.
How often should I add algaecide?
Only as often as the label's maintenance directions say, and only if you need it. With free chlorine kept at the minimum for your CYA, many pools need none.
Do I need algaecide if my chlorine is right?
Usually not. Chlorine kept above the minimum for your stabilizer level prevents algae. Algaecide is an extra safeguard for pools where chlorine is hard to keep up.
How long after adding algaecide can you swim?
Follow your product's label. The five labels we read all say to wait 15 minutes, but check yours. If you also added chlorine, wait until free chlorine is at or below the swim limit on that label.
Sources
- U.S. EPA, Poly-60 algaecide label, Reg. No. 48520-17 (polyquat 60%): epa.gov (PDF)
- U.S. EPA, BioGuard Algae All 60 label, Reg. No. 5185-339 (polyquat 60%; will not foam): epa.gov (PDF)
- U.S. EPA, Maquat YMCA label, Reg. No. 67262-34 (40% quat; may foam): epa.gov (PDF)
- U.S. EPA, HTH Algaecide label, Reg. No. 1258-1077 (10% quat): epa.gov (PDF)
- U.S. EPA, BioGuard Banish label, Reg. No. 5185-474 (copper; staining warning): epa.gov (PDF)
- CDC, Home pool and hot tub water treatment and testing: cdc.gov
- Dose formula: label scaling; see methodology.