How to Acid Wash a Pool: When It's Needed and What It Costs

Q: How often should a pool be acid washed?

Acid washing should be done only when necessary — not on a schedule. Each acid wash removes a thin layer of plaster (typically 1/32 to 1/16 inch). A pool has a finite number of acid washes before the plaster becomes too thin to sustain another treatment. Most pools can tolerate 3–5 acid washes over their lifetime, spaced years apart depending on water chemistry and staining.

Q: What does acid washing actually do to the pool surface?

Muriatic acid reacts with the calcium compounds in plaster (calcium carbonate, calcium silicate). The reaction dissolves the surface layer of plaster along with embedded stains, algae roots, calcium scale, and discoloration. The fresh plaster surface exposed underneath is lighter in color and more porous — which is why proper water balance after acid washing is critical.

📅 October 25, 2025Equipment⏱ 8 min read

Acid washing is a significant service — not a routine maintenance item. It drains the pool, removes a layer of plaster surface, eliminates embedded stains and algae, and resets the surface to something close to its original condition. It's the right call in specific situations, and the wrong call in others. Understanding when to recommend it, how to do it correctly, and how to price it is a core competency for service professionals.

When Acid Washing Is the Right Call

Acid washing is indicated when chemical treatments in water have failed to resolve surface conditions:

Severe algae staining — black algae that has penetrated the plaster surface and cannot be removed with brushing and shocking
Metal staining (copper or iron) that covers large areas of the pool surface after attempts with metal sequestrants and stain removal products have failed
Organic staining (tannins, leaf debris) that has deeply penetrated the plaster and resists chemical stain removal
Calcium scale buildup covering significant portions of the pool surface (scale that a pumice stone or calcium sequestrant can't address)
Reopening after extended abandonment — a pool that has been sitting without treatment for a year or more typically needs an acid wash to restore the surface before normal operation can resume

When Acid Washing Is Not the Right Call

Minor spot staining — localized stains on plaster respond to spot treatment (ascorbic acid for metal stains, calcium inhibitors for scale spots) without requiring a full drain
Plaster that's already very thin — older pools that have been acid washed multiple times may not have enough remaining plaster for another treatment. Rubbing a coin on the surface: if plaster is powdery or flaking, it's likely too thin
Vinyl liner or fiberglass pools — acid washing is a plaster treatment only. Both vinyl and fiberglass require completely different surface treatment approaches
Chemical imbalance as the root cause — if the pool has ongoing chemistry problems (chronic high pH, high calcium, poor circulation), acid washing treats the symptom but not the cause. The staining will return.

The Acid Wash Procedure

Muriatic acid (hydrochloric acid) is a corrosive chemical that produces toxic fumes. Wear chemical-resistant gloves, acid-rated goggles (not just safety glasses), rubber boots, and a respirator rated for acid fumes. Never work in an enclosed space. Keep soda ash (sodium carbonate) on hand for neutralization and first aid. Have a garden hose with running water accessible at all times.

Step 1: Drain the Pool

Use the pump on waste setting or a submersible pump to drain the pool completely. Never leave a pool empty for extended periods — hydrostatic pressure from groundwater can lift or crack an inground pool if it's empty and the water table is high. Plan to complete the acid wash and begin refilling the same day.

Step 2: Prep the Surface

Once drained, use a pressure washer to remove loose debris, algae, and dirt from the surface. This maximizes acid contact with the actual stains. Hose down the pool walls and floors and remove any standing debris with a brush.

Step 3: Mix and Apply Acid

Standard acid wash concentration: 1 part muriatic acid to 3 parts water (33% acid solution). Always add acid to water, never water to acid. Work in sections:

Wet the pool surface with water from the hose
Apply the acid solution to a 6–8 foot section of wall using a plastic watering can or acid sprayer
Allow to fizz for 30–60 seconds — the fizzing is the acid reacting with calcium in the plaster
Scrub with a stiff acid-resistant brush (not metal)
Rinse thoroughly to the drain sump at the bottom of the pool
Move to the next section; work around the walls top-to-bottom, then the floor

Step 4: Neutralize and Pump

After completing the wash, broadcast soda ash (sodium carbonate) across the pool floor: approximately 2 lbs per 1,000 square feet of surface. This neutralizes the acid waste water collecting in the pool sump. Use a submersible pump to remove the neutralized waste water.

Step 5: Final Rinse and Refill

Rinse the entire pool surface thoroughly with clean water before refilling. Begin filling immediately to prevent the plaster from drying, which can cause cracking. During the first 48 hours of filling, leave the pump off and let the water level rise naturally.

Chemistry After Acid Washing

Fresh plaster exposed by acid washing is highly alkaline and will dramatically affect the fill water chemistry:

Parameter	Expected Direction After Fill	Action
pH	Very high (8.0–9.0)	Add muriatic acid to bring to 7.4–7.6
Total Alkalinity	Very high	Add acid to lower; takes multiple treatments
Calcium Hardness	Low (fresh water) then rising	Monitor; new plaster leaches calcium
Free Chlorine	Low	Add maintenance dose; add CYA after 2 weeks

Do not add CYA for at least 2 weeks after acid washing — new plaster needs time to cure and the pH will be unstable during this period. Log every chemistry reading in PoolLens after acid washing, as the post-wash chemistry period is the most intensive maintenance window a plaster pool will experience.

Pricing Acid Wash Services

Acid washing is a premium service. Price components:

Labor: 4–8 hours for a typical residential pool (one technician for small pools; two for larger)
Materials: muriatic acid (2–4 gallons), soda ash (10–20 lbs), disposable PPE
Waste disposal: acid waste water disposal must be handled per local regulations — not all municipal systems accept pool acid waste
Market rate: $350–700 for standard residential (15,000 gallons), $700–1,200 for larger pools or severe staining

Document Acid Wash History and Post-Wash Chemistry in PoolLens

Log the wash date, plaster condition before and after, and the full post-wash chemistry recovery timeline. This record is essential for the next service provider who takes over the account — and for knowing when the pool is approaching its final acid wash.

Open PoolLens Free →

Frequently Asked Questions

How often should a pool be acid washed?

Only when necessary — not on a schedule. Each acid wash removes a thin layer of plaster. Most pools can tolerate 3–5 acid washes over their lifetime, spaced years apart. Never acid wash as routine maintenance when chemical treatment in water is sufficient.

Can you acid wash a vinyl liner pool?

No. Acid washing is a plaster/concrete surface treatment only. Muriatic acid will dissolve vinyl liner material and cause irreparable damage. Vinyl liner pools with staining require liner-compatible stain removers and specialized cleaning methods.

What does acid washing actually do to the pool surface?

Muriatic acid reacts with the calcium compounds in plaster, dissolving the surface layer along with embedded stains, algae roots, calcium scale, and discoloration. The fresh plaster surface exposed underneath is lighter and more porous — which is why proper water balance after acid washing is critical.

How much does a pool acid wash cost?

Professional acid washing typically costs $350–700 for a standard residential pool, depending on pool size, stain severity, and regional labor rates. This includes the drain, acid treatment, neutralization, scrubbing, and waste disposal. Refilling adds water cost.