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Dolphin Pool & Spa

Dog Days Algae: Why August Heat Breeds Green Water Faster

Published August 6, 2026

Pool algae prevention during Minnesota August heat

Images are AI generated and do not depict an actual pool or Dolphin Pool & Spa location.

August heat pushes pool problems into fast motion. Water that looked clear on Monday can turn cloudy by Thursday. Here is why algae grows faster right now, and how to stay ahead of it.

1 Why August Heat Breeds Algae Faster

Algae is a plant. Like any plant, it grows faster in warm water. Once your pool crosses the low 80s, algae cells split more often. A pool that held steady all June can turn green in two days once the heat sets in.

Heat also works against your chlorine. Strong August sun breaks down chlorine faster than the mild sun of June. Your sanitizer burns off before it finishes its job. Less chlorine on guard, more heat pushing algae to grow — both problems hit at once.

2 Signs You're Losing the Race

  • Water looks hazy instead of clear
  • Steps feel slippery underfoot
  • Green tint shows first in shaded corners
  • Chlorine reads low again a day after you added it
  • An algae smell replaces the usual chlorine smell

3 The Fix: Lead With Algae Complete

BioGuard Algae Complete is our first call for algae problems this time of year. It kills existing algae and keeps new algae from taking hold. Add it as soon as you see color changing — don't wait for full green water.

Back Up algaecide is a lower-cost option for owners who want basic prevention and don't need the stronger fix Algae Complete provides.

4 Test More Often This Month

August heat changes your water fast. Test twice a week instead of once whether in the store or with test strips. This will allow you to catch a chlorine decrease before algae gets a start.

Water testing costs $7 at our store. It's included when you buy $50 or more in chemicals the same visit.

5 Time Your Shock Right

Shock breaks down fast in direct sun. Add it at dusk or after dark, once the sun stops hitting the water. Shock added in full afternoon sun burns off before it can work. Stay out of the water for the time listed on the product label after shocking.

Quick Reference: Dog Days Checklist

Do

  • Test twice a week
  • Add Algae Complete at the first color change
  • Shock at dusk
  • Run your filter full time during heat waves
  • Brush walls and steps weekly

Don't

  • Wait for full green water to treat it
  • Shock in direct sun
  • Skip testing because water "looks fine"
  • Let a busy weekend skip a test
  • Ignore shaded corners

Early Summer vs. Dog Days: What Changes

Factor Early Summer (June) Dog Days (August)
Water Temp Upper 70s Mid-80s and up
Sun Strength Moderate Strong, longer daily exposure
Chlorine Burn-Off Standard rate Faster, needs more frequent doses
Algae Risk Low to moderate High
Recommended Testing Once a week Twice a week

Green water moves fast in August heat. If your pool tips over before you catch it, call Dolphin Pool & Spa. We'll test your water, help you pick the right fix, and get your pool back to clear — because we make pool ownership a joy!

Call Us Now — 763-542-9000

3405 Hwy 169 N, Plymouth, MN 55441

Your Happy Dolphin Pool & Spa Team