A drained pool is cleaned with a chem wash — an acid wash for calcium scale, mineral and metal stains and a rough, dingy surface, or a chlorine wash for algae, mold, and organic stains. The surface is wet down, the solution is applied in sections, scrubbed, rinsed, neutralized, and pumped out, then the pool is refilled right away. Waterline tile is cleaned in the same visit while the pool is empty. An acid wash removes a thin layer of finish each time, so it is a once-every-several-years treatment, not routine maintenance.
Acid wash vs. chlorine wash: which one?
| Acid wash | Chlorine wash | |
|---|---|---|
| What it is | Diluted muriatic acid applied to the drained surface | A strong chlorine solution applied to the drained surface |
| Fixes | Calcium scale, hard-water haze, metal and mineral stains, a rough or dingy finish | Green, black, and yellow algae, mold, organic (leaf, tannin) staining |
| How it works | Dissolves a very thin layer of the finish, taking the stain and scale with it | Kills and bleaches organic growth without removing finish |
| Effect on the surface | Brightens, but removes material — do it sparingly | Gentler on the finish; doesn't remove scale |
| Best for Valley pools | The hard-water pool with white crust and gray haze | The pool that went green and stayed stained |
Not sure which you need? The chlorine-tablet test from our algae guide works here too: if a stain lightens under a tablet it's organic (chlorine wash); if it doesn't, it's mineral (acid wash). Some pools need both. We'll tell you on a free visit, and honestly, the price is in the same range either way — one isn't the "budget" option.
How a chem wash is done.
- Drain to the right place. Most Valley cities require pool water to go into the home's sewer cleanout. Not the street, not the wash behind the house.
- Protect everything. Pump and filter are isolated so wash water never enters the equipment. The crew wears acid-rated gloves, eye protection, and respirators.
- Wet the surface. A dry surface drinks the solution unevenly and streaks. Everything is hosed down first.
- Apply in sections, top to bottom. The wash goes on a few feet at a time, is scrubbed with a brush, and is rinsed before it can sit too long. Working fast is the skill — leave acid on a spot and you get a bleached patch.
- Neutralize and pump out. Acid wash water is neutralized with soda ash before it's pumped to the cleanout. It never goes into the yard or storm drain.
- Clean the tile. With the pool empty, the waterline tile is bead-blasted or scrubbed to remove calcium scale — more on that below.
- Refill immediately. Hoses go in the same day. An empty pool in Arizona sun shouldn't wait — see how long a pool can stay empty.
- Startup chemistry. Fresh fill water in the Valley is hard and high in alkalinity. It gets balanced before the surface has a chance to scale again.
Why the tile gets cleaned in the same visit.
That white, crusty line at the waterline is calcium scale from our hard water. It builds up a little with every inch of evaporation, and it doesn't scrub off with a sponge. Cleaning it properly means lowering the water or draining, then blasting the scale off with fine glass bead or similar media — which is exactly why we do it while the pool is already empty for a wash. One drain, both jobs. We don't do stand-alone tile cleanings without a chem wash, because it's not the best use of your money.
Should you do it yourself?
You can buy muriatic acid at any pool store, and plenty of homeowners have acid washed a pool. The risks are real, though: acid fumes in an enclosed shell, burns, bleached streaks from uneven application, drained water in the wrong place, and the one we see most — a pool left empty in the heat for a week while the project drags on. If you go the DIY route: cool day, two people, full protection, soda ash on hand, and refill the same day.
When a wash isn't enough. If the surface is rough enough to scrape your feet, pitted, or showing bare shell, an acid wash will brighten it for a season and then it's back. At that point the honest answer is a pebble resurface — and the drain you'd do for a wash becomes the drain for the remodel.
How often is too often?
Every acid wash removes a little finish. On a pebble surface that's fine every several years; on a thin or old finish it can expose the shell. Chlorine washes are gentler. Most Valley pools pair a chem wash with the drain they need anyway every three to five years for water quality, and that cadence works well.
