Also called a drain & clean, an acid wash becomes necessary if the pool has turned into the "black lagoon". This may occur if the winterizing process is not done properly, or if the pool has been stagnant for a period of time so that algae has taken over, or if it’s filled with leaves and debris.

Our general rule of thumb for determining the need for an acid wash is: if you can see the bottom of the pool (the floor) then you can bring it back with chemicals, cleaning and filtering. If the floor is not visible, the cost of the chemicals and labor will generally be greater than the acid wash charge, and take much, much longer. Also, extensive algae blooms will stain plastered pools, making an acid wash desirable.

An acid wash is a purposeful stripping of a thin layer of plaster, exposing fresh plaster beneath. Therefore, it is ill-advised to make it an annual custom, which will accelerate the need for re-plastering. Most plaster coats (sometimes called whitecoat or marcite) are in excess of 1/2", so a careful acid wash every few years won’t hurt.

You may also decide on an acid wash not because of swamp conditions, but just to bring out a brighter, whiter finish. Mineral stains and/or deposits, chlorine stains, even dirt acid wash is always a dramatic aesthetic improvement to a plastered pool or fountain.

If your pool has had years of algae blooms, and if your pool seems to grow algae overnight or just bloom very easily... changing the water and acid washing the surfaces can give you an algae-free summer. Changing the filter media at the same time is also recommended.

Muriatic Acid is a dangerous substance. Alternatives exist that are low fume and less hazardous to work with. All personnel should be trained in safe acid application and wear protective clothing and breathing apparatus during an acid wash. To protect our environment, the acid/water waste should be neutralized with pH increaser prior to being pumped to a safe location.

If you decide to drain and clean your own pool, make sure that the hydrostatic relief plugs are removed as soon as possible, and that the water is pumped to a distant location, or into a storm drain, so that it won’t cycle beneath the pool. If your pool sits in a topographically depressed area, or if you have a high water table, or heavy recent rainfall, be extra careful with managing the hydrostatic pressure under the pool. You may also need to check with local water authorities for waste water discharge regulations in your area. Move the discharge hose regularly as needed, to avoid oversaturation and erosion of any area.

STEP 1: As you drain the pool, wash it down (scrub or use a push broom if necessary) to remove all algae and leaves. If you let the algae (and other gunk) dry on the surface, it becomes twice as difficult to remove. Spray the surface with a nozzle (walls, then floor) as the water level drops, before it dries into a baked-on finish. When all of the water is removed, bag up all leaves and debris in the pool's bottom.

When the pool is clean and empty, you can begin to acid wash the plaster. Put on protective clothing and rubber boots, goggles and wear a breathing mask designed for acid fumes.

STEP 2: Add equal parts acid to water in a flower watering can with a long pouring spout. (Always add acid to water, never the other way around). A weaker solution can be used, try to use as little acid as possible, to avoid damage to the plaster. Moisten the wall with a hose before you pour acid, avoid pouring the acid mixture on dry surfaces. Keep the hose running at all times, without a nozzle. Pour the acid/water mixture down the wall, from top to bottom, one section at a time. Do not allow the acid to sit on the plaster for very long. Usually 30 seconds is long enough. Use an acid brush to scrub stained surfaces and to move the acid around. Rinse quickly and thoroughly.

Make sure acid is rinsed completely, as it will continue to etch the plaster. Also try to prevent the acid from wearing a channel path on the floor from shallow end to deep end. Keep pushing the acid around, spreading it with hose and a large push broom or acid brush, to keep it moving while diluting the mixture.

If the 50/50 mixture isn't strong enough, you can increase the acid strength or the hang time (before rinsing), or you can scrub harder. Pools can also be acid washed a second time with a weaker mixture, or ‘spot wash’ areas that are still stained.

Remember that you don't want to damage or "burn" the plaster, by using too strong of a mix, or letting it sit too long. Horizontal surfaces like steps or swim outs need a triple-rinse; to be sure all of the acid is washed away. Acid does not deplete itself; it continues to corrode, until completely diluted or washed off.

STEP 3: After the acid wash, the bottom of the pool will be filled with a foamy, acid puddle. This needs to be neutralized before pumping out. It’s best to neutralize as you go, using about 2 lbs of soda ash per 1 gallon of acid used. Broadcast the soda ash (pH increaser) over the waste water puddle while stirring with a pool brush on a pole.

STEP 4: Use a small submersible pump with a hose to pump out the remaining acid water. Run the discharge hose up the shallow end floor if your pump is having trouble lifting water out of the deep end. Be careful where you pump the acid wash waste water. Even if properly neutralized, it can destroy plants or kill animals.

Rinse the deep end bowl with water again, and if needed, re-pour the bowl to clean up well around the drain, being careful with the strength, and diluting with lots of rinse water within 60 seconds. After the bowl is cleaned, begin to fill the pool, remembering to close any hydrostatic relief valves or plugs that were opened.

ACID WASH SAFETY: Don't rush the job and be safe. The fumes can be very strong, and very dangerous. Be sure to wear a respirator that will block muriatic acid fumes, goggles or safety glasses and protective clothing. Wear old shoes, or rubber boots. Spray off before exiting the pool.

Transporting the acid from the store to the house can be hazardous also. Secure the load in the vehicle. Always have a second person nearby when acid washing the pool. If acid drops enter the mouth or eye, rinse with the hose for 15 mins, without a nozzle on it. Acid on the skin won't usually burn too much, just rinse quickly, for 30 seconds.

Falling into empty pools is another hazard of acid washing. Take care that the deck area around the pool is clear and free of trip hazards, and that all personnel are aware of the danger of falling into an empty pool.

VINYL LINERS: If your pool is vinyl lined, acid is NOT used to clean vinyl. Small amounts of detergents and good 'ol elbow grease will remove the "slime". If drained completely, an inground vinyl liner must then be reset with a vacuum to ensure proper fit during filling. For this reason, liner pools are normally not drained completely if it can be helped, as there can be problems getting the liner to reset properly, and there is the rare danger of the walls buckling. Half-draining (to within 6” above shallow end floor) and refilling, while removing leaves and debris can often make a large difference in the speed and success of turning around a vinyl lined ‘black lagoon’ pool.

ACID WASH PRICES: Complete drain & clean charges average $500 for a residential pool. Higher costs may be seen for large amounts of debris in the pool, excessive neglect, or larger sized pools. Lower costs will be realized for clean or empty pools, or localized acid washing. If your water is from a well, you may elect to refill the pool with trucked-in water. Expect to pay about $200 per 5,000 gallons. If you refill from the hose; water costs are a few bucks per thousand gallons. Contact your Water Authority to let them know you are filling the pool and they may not charge you for the sewer, only the water portion of the bill.

Related Product Pages:

Acid Brush
Acid Magic
pH Increaser
Plaster Repair Kits

Related Blog Posts:

Acid Burned Pool Plaster
Acid Washing your pool Safely
How do I drain my pool?
Opening a Pool Neglected for YEARS