What an acid wash actually does
An acid wash drains the pool and applies diluted acid to the plaster surface, dissolving a very thin layer of the finish along with whatever staining is sitting in it. The stain does not come off the plaster — the plaster comes off with the stain.
That is why it works so well on old, mottled, mineral-stained finishes, and why doing it repeatedly is how a 15-year plaster job becomes a 9-year plaster job. Most finishes tolerate only a handful of washes across their life before aggregate is exposed and the surface turns rough.
Things worth trying first
Identify the stain before touching it. Organic stains from leaves and acorns often lift with chlorine and brushing alone. Metal stains from iron or copper usually respond to an ascorbic acid treatment with a sequestering agent, no draining required.
Scale is not a stain. White crust at the tile line is calcium carbonate and needs bead blasting or a specialty calcium removal crew, not acid on the plaster.
A sustained period of correctly balanced water sometimes does more than people expect. Water that has been slightly aggressive for years leaves a dull, chalky surface that looks stained but is really etched — and no wash fixes etching.
When an acid wash is genuinely the right call
After a long green-to-clean where the pool sat dead for months and the plaster is permanently discolored below the waterline.
Before a home sale, when the finish is otherwise sound and the discoloration is what buyers are reacting to.
When a pool is being drained anyway for high cyanuric acid or a refill, and the surface is already scheduled to be exposed.
The Central Texas cautions
Draining a pool in this area is not risk-free. Our soils move, and an empty shell in a high water table or after heavy rain can lift or crack. Draining is done with the ground conditions in mind, and never left empty in the sun any longer than the work requires.
Acid must be neutralized and the wastewater handled to local rules — it does not simply go into the street or a storm drain.
Plaster work and acid washing are outside what we do in-house. If your pool needs one, the honest answer is a referral to the right crew, plus water chemistry afterward that stops it from happening again.
