Pool Acid Wash in Milpitas, CA

Pool plaster is mostly calcium carbonate, the same stuff as limestone. Acid dissolves it. An acid wash puts a diluted acid on the bare, drained surface, and it eats away a very thin layer of plaster along with whatever is stuck in it.

That’s why it works on stains nothing else will touch. It’s also why it can’t be done over and over. Each wash leaves the plaster a little thinner, so the goal is to take off only as much as the stain needs.

Done right, the result is a brighter, more even surface. Done carelessly, with acid that’s too strong or left on too long, it leaves plaster rough, blotchy and older than it was.

Signs Your Pool Needs an Acid Wash

• Stains that stay put after brushing and a stain treatment
• Gray or white scale that makes the plaster feel rough
• Dark blotches left behind after a green pool was cleared
• A dull, patchy finish that looks dirty in perfectly clear water
• Rust-colored or brown spots from metals in the water

One or two small spots rarely justify draining the whole pool. An acid wash makes sense when the staining covers enough of the surface that spot treatments can’t keep up.

Pool Stain Removal: Find the Source First

Before any stain comes out, it helps to know what put it there. If the cause is still in the water, new stains show up after the wash, sometimes within weeks.

Metal stains are the most common kind. Iron, copper and manganese are the usual culprits. Copper often comes from a heater or other copper parts being eaten away by water with low pH. Iron can come from the fill water, and it tends to leave reddish brown stains. Copper can also bond with stabilizer and leave a faint violet tint.

So step one is testing the water for metals and checking the pH history. A metal sequestering product and steady water balance keep new stains from forming.

Metal Stains vs Organic Stains

Not every dark spot needs acid. Leaves, acorns and other plant matter that sit on the floor leave brown stains from tannins. Those stains are organic, and chlorine can often bleach them out without draining anything.

A quick test tells the two apart. Rub a chlorine tablet on the spot for a few seconds. If it lightens, the stain is organic. If nothing happens, try a little ascorbic acid, the powdered vitamin C used for metal stains. A spot that fades with that is a metal stain.

Knowing which one you have can save the cost of an acid wash entirely.

Calcium Scale on Plaster

Scale is a crusty white deposit, often gray from the dirt it traps. It forms when pH, alkalinity and calcium are all running high, and it builds up fastest where water evaporates. It feels rough underfoot and can scrape skin.

Heavy scale across the plaster is one of the main reasons for an acid wash. Scale along the waterline is a different job. For that band on the tile, see our pool tile cleaning page.

How to Acid Wash a Pool

1. Test the water and figure out what caused the stains.
2. Check the hydrostatic relief valve, then drain the pool.
3. Rinse the walls and floor and clear out debris.
4. Mix muriatic acid with water and work in small sections, top to bottom.
5. Brush each section, then rinse it quickly so the acid can’t bite too deep.
6. Neutralize the acid water in the deep end with soda ash before pumping it out.
7. Rinse again, check the surface, then refill.
8. Balance the new water and restart the equipment.

Timing is the skill here. Acid left on for too long etches the plaster, and a section rinsed too early leaves the stain behind.

Why Draining Takes Care

An empty pool is lighter than the ground water around it. When that water is high, it pushes up on the pool shell and can crack it or even lift it out of the ground. Many in-ground pools have a hydrostatic relief valve in the floor for this reason. It opens and lets ground water in before the pressure gets dangerous.

We check that valve before draining. It’s also smart to avoid draining right after a stretch of heavy winter rain, when the soil is soaked.

Where the water goes matters too. Storm drains run straight to creeks and the Bay with no treatment, so pool water and acid rinse water don’t belong in them.

Muriatic Acid Safety

Muriatic acid is hydrochloric acid. The NIOSH guide to hydrogen chloride lists burns to the eyes and skin, plus irritation of the nose, throat and lungs, as its main hazards. That’s why an acid wash calls for goggles, acid-resistant gloves, boots and a respirator, plus plenty of rinse water close by.

Always add acid to water, never water to acid. Keep kids and pets out of the backyard until the job is done and the acid water is neutralized.

Acid Wash vs Chlorine Wash

A chlorine wash is the gentler cousin of an acid wash. Instead of acid, a strong chlorine solution goes on the drained surface. It bleaches algae and organic stains well but does little to mineral stains or scale.

If the problem is mostly leftover algae staining after a green pool, a chlorine wash may be all it needs. For metal stains and scale, acid is the tool that works.

Which Pool Surfaces Can Be Acid Washed

Standard white plaster, sometimes called marcite, is what an acid wash was made for. Colored plaster can be washed, but the acid may lighten the color unevenly, so it calls for a weaker mix.

Pebble and quartz finishes can take an acid wash, but gently. Too much acid loosens the pebbles or leaves sharp edges. Fiberglass and vinyl liner pools should never be acid washed, since the acid damages the gelcoat or the liner.

Refilling and Starting Up After an Acid Wash

Freshly washed plaster is sensitive for the first few weeks. The new water needs to be balanced quickly and kept there. Water that’s low in calcium or alkalinity pulls calcium out of the plaster and can etch it, which undoes some of the work.

After the refill, the water gets tested and adjusted, and the filter runs to catch any plaster dust. Brushing daily for the first week helps too. Pools on our weekly pool service get those checks at every visit.

While the Pool Is Empty

A drained pool is the easiest time to deal with things that are hard to reach underwater. It’s a good moment to look for cracked or loose tile, check the main drain covers and replace a failing light, lens or gasket.

Small plaster chips and cracks are easier to see, too. Anything we spot goes on the list so you can decide what to fix before the water goes back in. For new lights, see pool light installation.

When an Acid Wash Isn’t Enough

An acid wash can only remove what sits near the surface. Stains that run deep into old plaster, heavy etching, plaster that’s flaking or bare spots showing the gunite underneath all point to replastering instead.

A pool that has already been acid washed several times is also near the end of what it can take. At that point, another wash just thins the plaster further. We’ll tell you if that’s where your pool is.

Acid Wash Pool Cost

Acid wash pricing comes down to pool size, how heavy the staining is and how much scale has to come off. The surface type matters too, since pebble finishes and colored plaster call for more careful work.

Draining, washing, neutralizing, refilling and balancing are all part of the job. Your free quote spells out what’s included before any water comes out of the pool.

Keeping Plaster Clean After an Acid Wash

• Keep pH, alkalinity and calcium steady, since both scale and etching start with unbalanced water.
• Use a metal sequestering product if your water carries iron or copper.
• Pull leaves and debris off the floor before they stain.
• Brush the walls and floor every week.
• Fix a low pH quickly, because corrosive water eats heater parts and puts copper in the pool.

Booking a Pool Acid Wash in Milpitas

To get on the schedule, phone (408) 317-7550 or use the request form. Photos of the stains help, along with the finish type if you know it. Acid wash jobs run across Milpitas and every city in our service area. For the other jobs weekly cleaning can’t cover, see our specialty pool services.