In most of the country, a neglected pool takes weeks to turn green. In Phoenix in July, it can happen over a long weekend. If you’ve come home from vacation to a swamp, you’re not alone — here’s what’s actually happening in the water, and how to stop it for good.
The 3 Real Causes of Green Pools in the Valley
1. Heat and UV Destroy Chlorine at Astonishing Speed
At 95°+ water temperatures under intense UV, free chlorine gets consumed several times faster than in spring. A pool that held chemistry fine in April can burn through its entire sanitizer reserve in two or three days in July. Once free chlorine hits zero, algae — whose spores are always present — bloom explosively.
2. CYA Lock: Too Much of a Good Thing
Cyanuric acid (stabilizer) protects chlorine from UV — but every tablet of trichlor adds more of it, and in Arizona, evaporation concentrates it. Above roughly 100 ppm, CYA starts binding chlorine so effectively that your test shows chlorine present while almost none of it can actually kill anything. Pools in ‘CYA lock’ turn green with seemingly fine chemistry, and the only real fix is a partial drain and refill.
3. Circulation Failures
A tripped breaker, a failed pump capacitor, a clogged impeller, or a timer knocked out by a power flicker — in summer heat, 72 hours without circulation is usually enough to start a bloom. This is why equipment checks matter as much as chemicals — a quick pool equipment repair beats a week of algae treatment.
How to Prevent It
- Test water at least weekly in summer — more after storms
- Keep CYA in the 30–80 ppm range; if you’re over 100, plan a partial drain (ideally in cooler months)
- Run the pump 8–12 hours daily in summer
- Glance at your equipment pad twice a week — is the pump actually running?
- Keep the filter healthy: pressure 8–10 PSI over baseline means clean it
Already Green? Here’s the Honest Truth
A mild green haze can often be recovered with a heavy shock, brushing, and filter cleaning over a few days. A full bloom — opaque green, can’t see the first step — usually needs professional-grade treatment, repeated filter cleanings, and several visits. And a black-algae or long-neglected pool sometimes makes more financial sense to drain and deep clean. A good pool company will tell you which one you actually have instead of selling you the most expensive option.
Aqua Shine’s green pool cleanup service clears most Phoenix pools in 3–7 days, with upfront pricing and an honest drain-vs-treat recommendation. And if you’d rather never fight algae again, our weekly pool service in Phoenix keeps chlorine ahead of the heat all summer.
Need a hand from a local pro? Aqua Shine Pools serves Phoenix, Scottsdale, and the West Valley with weekly service, repairs, and rescues — call (480) 788-9772 or request a quote.