Algaecide Dosing Calculator
Calculate exactly how much algaecide to add to your pool for weekly prevention, season opening, or an active bloom — with step-by-step guidance for treating green, yellow (mustard), and black algae. Enter your pool volume and algaecide type for the precise dose.
Algaecide Type
Check your algaecide bottle label for the active ingredient percentage. Polyquat 60% is the most common residential choice — it's non-foaming and compatible with all sanitizers.
Treatment Purpose
Preventive doses are added weekly to stop algae before it starts. Use Initial/Opening at the start of the season. Use Outbreak dosing only when visible algae is present — follow up with shock and brushing.
The total water volume of your pool in gallons. Check your pool builder's paperwork, or estimate using: length × width × average depth × 7.48.
Algaecide to Add
Add directly to the pool with the pump running. For best results, pour around the perimeter rather than in one spot.
💡About this calculator▼
Getting the algaecide dose right matters — too little and algae comes back within days, too much wastes money and, with copper, can permanently stain your pool. This calculator uses actual EPA-registered product label rates for each algaecide type to give you the correct amount for your pool size and situation. It also walks through how treatment differs for green, yellow (mustard), and black algae — because the tougher two need aggressive brushing and shock, not just a bigger dose.
The calculator looks up the standard dosing rate for your algaecide type and treatment purpose (in fluid ounces per 10,000 gallons), then scales it to your pool volume. Rates are based on real EPA-registered product labels for each algaecide class — not generic estimates.
📐How it's calculated▼
Amount (fl oz) = (Pool Volume ÷ 10,000) × Dose Rate
Dose rates per 10,000 gallons by product type:
• Polyquat 60%: 3 oz (prevention), 8 oz (initial/opening), 11 oz (active algae)
• Polyquat 30%: 6 oz (prevention), 16 oz (initial/opening), 22 oz (active algae)
• Quat 10%: 8 oz (prevention), 16 oz (initial/opening), 26 oz (active algae)
• Quat 50%: 1.5 oz (prevention), 5 oz (initial/opening), 5 oz (active algae)
• Copper-based (7%): 2 oz (prevention), 4 oz (initial/opening), 8 oz (active algae)
Rates follow EPA-registered product labels: In The Swim Algaecide 60 Plus and ProTeam Polyquat 60 (2–4 oz maintenance / 6–11 oz initial), In The Swim Pool Algaecide (10% quat) and In The Swim Algaecide 50 (50% quat, 5 oz initial / 1.5 oz maintenance), and In The Swim Super Algaecide / 7.1% chelated copper (2 oz maintenance / 4 oz initial). Important: Polyquat and copper labels do NOT call for a mega-dose to clear a bloom — for active algae you shock and brush first, then apply the high end of the normal range. Copper is kept deliberately conservative because over-applying it can permanently stain pool surfaces.
📎Source:EPA-registered product labels: In The Swim Algaecide 60 Plus, ProTeam Polyquat 60, In The Swim Pool Algaecide (10% quat), In The Swim Algaecide 50 (50% quat), In The Swim Super Algaecide (7.1% chelated copper)
🔍Finding your inputs▼
Pool Volume: Check your pool builder's paperwork or equipment manual — most list the volume in gallons. If you don't have it, a rough estimate is length × width × average depth × 7.48 for a rectangular pool.
Algaecide Type: Check your bottle's active ingredients label. Polyquat products list "poly[oxyethylene...]" as the active ingredient at 30% or 60% — these are non-staining and non-foaming. Quat products list a quaternary ammonium compound — pick the Quat 10% or Quat 50% option to match the percentage on your label, since a 50% quat is about 5× stronger and needs roughly a fifth as much. Copper-based products list copper sulfate or metallic copper.
Treatment Purpose: Choose Weekly Maintenance for routine prevention. Choose Opening/Initial at the start of the season. Choose Active Algae Outbreak only when you can see algae — combine with shock treatment and brushing.
⚠️Special situations▼
Green algae (the most common type)
Green algae is the easiest to beat and what most algaecides are built for. Brush the surfaces, shock the pool, run the filter continuously, then add an Active Algae Outbreak dose of algaecide (Polyquat 60% is the reliable choice). Keep free chlorine at 1–3 ppm and pH 7.2–7.6 afterward, and add a weekly maintenance dose to stop it coming back. A green pool usually clears within 24–48 hours of shock plus algaecide.
Yellow / mustard algae
Mustard algae is chlorine-resistant and clings to walls, steps, and shady corners, so an algaecide dose alone will not clear it. Brush aggressively (it returns from any spot you miss), shock at a higher-than-normal level, and add an Active Algae Outbreak dose. Then decontaminate everything that touched the water — swimsuits, toys, floats, the pole and brush, even the filter — or it reinfects within days. A Polyquat or a dedicated mustard/yellow algaecide handles this better than copper. Expect to repeat the brush-and-shock cycle a few times.
Black algae (the toughest)
Black algae roots into plaster and grows a protective cap, so pouring algaecide over it does almost nothing by itself. You have to physically break that cap first: scrub hard with a stainless-steel brush on plaster/gunite (use a stiff nylon brush on vinyl or fiberglass so you don't tear the surface), then shock heavily and apply an Active Algae Outbreak dose so the chemicals can reach the roots. Rubbing a trichlor chlorine tablet directly on stubborn spots helps. It is persistent — plan on repeating the scrub–shock–algaecide cycle over several days and keeping chlorine high until it's completely gone. The amount below is the algaecide portion only.
Copper-based algaecide with well water or high metal content
Copper algaecides can cause green or black staining on pool surfaces if your water already has high metal content. Test your water for metals first. If metals are elevated, use Polyquat instead — it's non-metallic and stain-free.
Active algae outbreak that doesn't clear after one treatment
If algae is still visible after 24 hours, brush all surfaces again, run the filter continuously, and re-shock — and check that chlorine and pH are in range, since algaecide works best at 1–3 ppm chlorine and pH 7.2–7.6. For Polyquat or Quat you can repeat the outbreak dose. For copper-based algaecide, do NOT keep re-dosing — repeated copper drives levels up and risks permanent staining; clear stubborn algae with shock and brushing instead, and rely on copper only for prevention.
Pool with attached spa or water feature
Copper-based algaecides can stain spa jets, decorative fountains, and tile grout. Use Polyquat 60% for pools with attached features — it's specifically formulated to be safe for these applications.
Quat 10% causing foam
Quat algaecides foam when agitated — this is normal. The foam is harmless and will dissipate within a few hours. If foaming is excessive, you may have overdosed or your pool has high organic load. Polyquat products are non-foaming if foam is a persistent issue.
❓Common questions▼
Does algaecide kill green, yellow, and black algae?
It helps with all three, but it isn't a standalone cure for the tough ones. Green algae usually clears fast with shock plus an algaecide outbreak dose. Yellow (mustard) and black algae are chlorine-resistant and need aggressive brushing and heavy shocking first — algaecide is the finishing and prevention step, not the main weapon. Black algae in particular roots into the surface and has to be physically scrubbed open before any chemical can reach it. Use the calculator for the algaecide amount, and pair it with the brushing-and-shock steps for the algae type you have.
What's the difference between Polyquat and Quat algaecides?
Polyquat (polymeric quaternary ammonium) algaecides are non-foaming, non-staining, and compatible with all sanitizer systems. They're the most popular choice for residential pools. Quat algaecides at 10% concentration are older-generation products that can cause foaming, especially at higher doses. Polyquat 60% is the most effective and hassle-free option for most pool owners.
Can I add algaecide and shock at the same time?
No — add shock first and wait at least 24 hours before adding algaecide. High chlorine levels from shock will break down many algaecide compounds before they can work. Shock kills most of the algae, then algaecide cleans up the rest and prevents regrowth.
How often should I add algaecide?
For prevention, once a week is standard — typically the same day each week after your regular pool maintenance routine. During hot weather, heavy use periods, or after heavy rain, consider dosing every 3–5 days since these conditions accelerate algae growth.
Why is the initial/opening dose so much higher than the maintenance dose?
Maintenance doses top off an existing chemical residual already present in the water. An initial dose has to establish that residual from scratch in water that contains none — which requires significantly more product. Using a maintenance dose for an opening treatment is one of the most common algaecide mistakes, leaving the pool unprotected in the first weeks of the season.
Is copper algaecide safe for vinyl liner pools?
Copper algaecide can stain vinyl liners if the pH is out of range or if the product is added undiluted. If you use copper algaecide in a vinyl liner pool, pre-dilute it in a bucket of pool water before adding, maintain pH between 7.4–7.6, and pour slowly around the perimeter rather than in one spot.
🔗 Related Calculators
Chlorine Dosing Calculator
Calculate exactly how much chlorine to add to your pool. Enter your pool volume, current and target free chlorine levels, and chlorine product type to get the precise dose.
Pool Shock Treatment Calculator
Calculate exactly how much pool shock or bleach you need. Supports HTH, calcium hypochlorite, and liquid chlorine for any pool size (e.g. 12,000 gallons).
Cyanuric Acid Dosing Calculator
Calculate exactly how much cyanuric acid (pool stabilizer) to add to raise CYA to your target level — or how many gallons to drain if CYA is too high. Includes minimum free chlorine guidance.