Every summer, our phone starts ringing with the same panicked question: 'I left for a long weekend and came back to a swamp - what happened?' In Houston, it's almost always the same combination: 95°+ heat, heavy pool use, and one of our fast-moving afternoon thunderstorms diluting chlorine and stabilizer all at once.
The good news - a green pool almost always comes back. Here's the exact rescue sequence our service techs run, plus how to keep it from happening again for the rest of the summer.
01Step 1 - Figure out why it turned
- Rain dilution - a couple inches of rain can cut chlorine and stabilizer levels in half overnight.
- Heat - chlorine burns off far faster once water temps push past 88–90°F.
- Filter neglect - a dirty cartridge or a filter that hasn't been backwashed in weeks can't keep up with summer bather load.
- Low run time - the pump needs 8–10+ hours a day in peak summer to turn the water over enough times.
Green water is really just algae that won the race against your sanitizer. Once you know the cause, fixing it is mostly patience plus the right order of operations.
02Step 2 - Rebalance before you shock
- Test and adjust pH to 7.2–7.4 first - shock works far better in this range.
- Brush every surface (walls, steps, ladder, behind lights) to break up algae clinging to the plaster.
- Run the pump continuously - don't turn it off until the pool clears.
03Step 3 - Shock aggressively (then wait)
A green pool needs a much bigger dose than a weekly maintenance shock - often 2–4× the normal amount, dosed at night so the sun doesn't burn it off instantly. Keep the pump running and don't be tempted to shock again after just a few hours; give it a full 12–24 hours to work before retesting.
04Step 4 - Filter it out
Dead algae doesn't disappear - it has to be filtered out. Expect to clean or backwash your filter multiple times over 24–48 hours as it clogs with the debris. This step is where most DIY green-pool fixes stall out because homeowners stop cleaning the filter and flow (and clarity) grinds to a halt.
The pool doesn't clear because you added more chemical - it clears because you kept the water moving and the filter clean long enough for the chemical to finish the job.
05When to call a pro instead of DIY-ing it
- The pool has been green for more than 3–4 days with no improvement.
- You've shocked twice and it's still cloudy or green-tinted.
- Metal staining (green-blue, not algae) appears on plaster or tile.
- You're heading out of town and need it swim-ready by a specific date.
06Preventing the next one
Keep stabilizer in the 30–50 ppm range through peak summer, run the pump a full cycle daily, and re-test chemistry after any rain event over an inch. If you're leaving town for more than a few days during the hottest stretch of summer, ask your service company for a pre-vacation check rather than hoping the auto-chlorinator keeps up alone.
Written by
Mike Lopez
Owner, Houston Cool Pools
Every article on this site is written from the field - from real builds, real remodels, and real service calls with Houston homeowners. If you're thinking about a project, we'd love to talk it through.
