Pool owners are often shocked by the speed. The pool was fine on Saturday and by Wednesday it is a pond. In Austin summer conditions, four days is completely ordinary — and the process started well before the colour changed.
The sequence
Day 0 — chlorine hits zero. Something consumed it: a hot week, a pool party, a storm, or simply nobody adding any. Sanitiser is now gone.
Day 1 — colonisation. Algae spores are already in every outdoor pool; they arrive on wind, rain and swimsuits. With nothing to kill them they attach to walls, steps and grout lines. The water still looks clear.
Day 2 — the water dulls. Not green yet, just slightly less sharp. This is the last cheap moment to intervene.
Day 3 — visible bloom. Free-floating algae multiplies exponentially. The water goes hazy green.
Day 4 — full green. The bottom disappears. Now it is a recovery job, not a chemistry adjustment.
What sets it off in Travis County
The February and March cedar and oak pollen bloom. For a few weeks every late winter, Central Texas air turns yellow. Pollen lands on the surface, sinks, and breaks down into phosphates — which is the single best fertiliser algae could ask for. Pools that were fine in January go cloudy in March for exactly this reason.
Hard freezes. Austin gets a handful of genuine freeze events each winter, and they are what break equipment here. Pumps, filters and exposed plumbing need to keep moving through a freeze; a pool left on a timer that shuts the pump off at 10pm during a hard freeze is how tanks crack.
Phosphates. Decaying leaves, pollen, fertiliser runoff and blown-in dirt all add phosphate, which is algae food. High phosphate does not cause a bloom on its own, but it makes one far harder to stop once chlorine slips.
Stabilizer that is too high. Cyanuric acid protects chlorine from the sun, but above roughly 80–100 ppm it locks chlorine up. The test kit reads chlorine present while the pool behaves as if there is none — a genuinely common and genuinely confusing failure here.
Stopping it instead of fixing it
The cheap version of this problem is a weekly visit where somebody tests the water, corrects it and brushes the surfaces algae would otherwise colonise. The expensive version is a recovery.
If your pool has gone green, it can almost always be brought back without draining. See how a green pool recovery works.
Would rather not do this yourself? Our complete weekly service in Austin starts at $159 a month with routine chemicals included and no contract. Get a free quote or call 512-640-4884.
