Polyquat 60 (polyquaternary ammonium chloride at 60% concentration) is the correct maintenance algaecide for most residential pools. It does not foam, does not contain copper that can stain surfaces, and works alongside chlorine. For black algae on plaster, copper-based products are more effective. For green algae already established, shock first — algaecide alone does not clear a green pool.
Algaecide is prevention chemistry, not treatment chemistry. If your pool is already green, shock is what clears it. Algaecide is what keeps it from going green again. Understanding which product to use in which situation — and what none of them can actually do — prevents wasted money and continued algae problems.
The Three Types of Pool Algaecide
Polyquat 60 (Polyquaternary Ammonium Chloride)
The standard weekly maintenance algaecide for most residential pools. Polyquat 60 refers to the active ingredient concentration: 60% polyquaternary ammonium chloride. Key characteristics:
- No foaming — lower-concentration quat products (10-30%) foam heavily. At 60%, foaming is not a practical issue with correct dosing.
- No copper — cannot stain pool surfaces or turn hair green. Safe for all pool surface types including vinyl and fiberglass.
- Broad spectrum — effective against green, yellow/mustard, and early-stage black algae.
- Works with chlorine — can be used in normally chlorinated pools without deactivating the sanitizer (at the correct timing — add only when FC is below 4.0 ppm).
- Weekly maintenance dose: typically 2-4 oz per 10,000 gallons per week depending on product label instructions.
Copper-Based Algaecides
Copper sulfate and copper chelate formulations are the most effective algaecides against black algae and resistant mustard algae. Copper disrupts algae enzyme systems in a way that chlorine alone cannot penetrate the protective head of black algae.
Critical cautions with copper-based products:
- Can stain pool surfaces green, blue-green, or teal — particularly plaster, grout, and vinyl — if levels become elevated or if the pool has high pH or low stabilizer.
- Copper accumulates in pool water — does not dissipate. Repeated copper algaecide additions over a season can build up to staining levels (above 0.3-0.5 ppm).
- Test copper levels before using copper algaecide if you have previously used it. Metal stains from copper require a metal treatment process and are not removed by standard chemicals.
- Not recommended for regular weekly maintenance use. Reserve for black algae or resistant mustard algae situations where polyquat has failed.
Sodium Bromide (Winter/Opening Algaecide)
Sodium bromide is used as an opening treatment and winterizing algaecide for extended closings (6+ months). It provides longer-lasting protection than polyquat at cold water temperatures where chlorine-based chemistry is less effective. It is not appropriate as a regular swimming season algaecide.
What Algaecide Cannot Do
| Claim | Reality |
| ‘Will clear a green pool’ | False. Algaecide slows algae growth but does not have the oxidizing power to kill an established bloom. Shock with cal-hypo first; add algaecide the next morning after FC drops below 4.0 ppm. |
| ‘Replaces regular shocking’ | False. Algaecide and shock address different problems. Shock oxidizes chloramines and kills established algae. Algaecide prevents re-establishment. Neither substitutes for the other. |
| ‘Works at any chlorine level’ | False. High free chlorine above 4-5 ppm rapidly oxidizes and deactivates quat-based algaecides before they reach algae. Always add algaecide when FC is in the normal 1-4 ppm range. |
| ‘Prevents algae indefinitely without chlorine’ | False. Algaecide is a supplement to chlorine sanitation, not a replacement. A pool with zero free chlorine will develop algae regardless of algaecide level. |
| ‘Works on black algae as well as green’ | Partially true. Polyquat 60 has some effect on early black algae, but established black algae requires copper-based products plus aggressive physical brushing to penetrate the protective head. Green algae respond well to polyquat maintenance. |
How to Use Algaecide Correctly
- Test free chlorine before adding — FC must be below 4.0 ppm. Adding algaecide to a pool immediately after shocking wastes the product.
- Add algaecide directly to the pool water near a return jet for distribution — not through the skimmer.
- Run the pump for at least 4 hours after adding to distribute the product throughout the pool.
- For weekly maintenance: add once per week at the standard label dose. Double the dose at pool opening, after heavy rain, or after treating a algae bloom.
- Do not mix algaecide with other chemicals in the same bucket or container.
✓ KEY FACT: The opening-season dose of algaecide matters more than the weekly dose. Adding a double dose of polyquat 60 at opening — before the pool has a chance to develop any algae — is significantly more effective than trying to control algae that has already started growing.
If X Happens, Do Y
I added algaecide and the pool foamed heavily
Two causes: (1) you used a low-concentration quat product (10-30%) rather than polyquat 60 — these foam significantly and are not appropriate for pools, (2) you added too much polyquat 60 at once. Foaming from polyquat 60 at correct doses is minimal. Run the filter and the foam will dissipate within 24-48 hours. To prevent: use only polyquat 60 concentration products and follow label dosing precisely.
I used copper algaecide and now my pool has green stains on the walls
Copper has precipitated onto the pool surface. This happens when copper levels exceed 0.3-0.5 ppm, particularly at elevated pH. The stains are permanent without a metal treatment protocol. Do not attempt to remove with acid — acid alone will not remove copper stains and may damage the surface. A professional metal stain removal process using a chelating agent (such as ascorbic acid treatment for copper stains) followed by a metal sequestrant is required. Test copper and metal levels before any further treatment. Stop using copper algaecide.
My pool keeps getting algae despite weekly algaecide
Algaecide is supplemental to chlorine — it cannot substitute for it. Check three things: (1) test CYA — if above 80 ppm, your chlorine is not effective enough regardless of algaecide, (2) confirm free chlorine is consistently above 1.0 ppm — algaecide at 0 ppm FC will not prevent algae growth, (3) confirm you are adding algaecide at the correct timing (FC below 4.0 ppm) so it is not immediately oxidized by high chlorine.