How to acidwash a pool

Published by Swimming-Pool-Expert on June 24th, 2011

Acid Washing

You will have to drain and clean your pool before you start. An acid wash becomes necessary if the pool has turned into a swamp. This may occur if the pool has been stagnant for a period of time so that algae has taken over.

The 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, labour and filtering. If the floor is not visible, the cost of the chemicals and labour will generally be greater than the acid wash charge, and take much longer. Also, extensive algae blooms will stain plastered pools, making an acid wash desirable and if there are any other stains maybe from metals.

An pool acid wash is, put simply, purposeful stripping of a tiny layer of liner, exposing fresh plaster beneath. Therefore, it is not advised to make it an annual custom, which will accelerate the need for re-plastering. Most plaster coats (sometimes called marble plaster or marblite) are in excess of 8mm, so a few careful acid washes should not 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 caused by excessive use of algaecides (such Pool Magic; Blue 52) may cause brown pool marks or staining. Sole use of calcium hypoclorite (HTH) could on the other hand cause buildup of white marks on the waterline or in severe cases a thick white calcium layer on the interior pool surface that could only be washed off by “normal pool acid”, that is hydrochloric acid sold in most retail chains like Makro; Builders Warehouse; Mica; Chaimberlains; Game; Pick N Pay; and Shoprite.

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 algae sticks to, can give you an algae free summer.


Acid is a dangerous substance. Pool company personnel are specially trained in its application and wear protective clothing and breathing apparatus during the acid wash. To protect our environment, the acid/water waste should be neutralized with soda ash prior to its being pumped to a safe location.

If you decide to drain and clean your own pool, make sure that the hydrostatic relief plugs are pulled as soon as possible, and that the water is pumped to a distant location, or into a storm drain. You may also need to check with local water authorities for waste water discharge regulations if there is.

As you drain the pool, wash it down (scrub if necessary) to remove all algae and leaves. Bag up all leaves and debris in the pool’s bottom. When the pool is clean and empty, you can begin to acid wash. Put on protective clothing and rubber boots, goggles and wear a breathing mask designed for acid fumes.

Add 2 litres acid to 2 litres water in a mixing or compresion can (Always add acid to water, never the other way around). Wet down the wall with a hose. Keep the hose(s) running at all times, without a nozzle on it. Pour or spray the acid/water mixture down the wall, from top to bottom, one 3 meter section at a time. Do not allow the acid to sit on the plaster for too long. Usually 30 seconds is long enough. Use a hard brush that is chemical resistant to scrub the surfaces and move the acid around. Rinse quickly and thoroughly.

Make sure acid is rinsed completely, as it will continue to eat into the plaster. Also try to prevent the acid from wearing a channel path from shallow end to deep end. This can create a worn stripe on the floor.

If the 50/ 50 mixture isn’t strong enough, you can increase the acid strength or the hang time (before rinsing) or scrub harder. Usually pools are acid washed twice with the same strength mixture.

Remember that you don’t want to damage or “burn” the plaster.

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. Use 500g of soda ash per 2 litres of acid used. Broadcast the ash over the puddle while stirring with a pool brush on a pole. Use a small submersible pump with a hose to pump out the remaining acid water. Be careful where you pump it to. Even if properly neutralized, it may destroy plants or kill fish, frogs, etc.

Rinse the pools’ deepend (or bowl) again and re-spray the bowl of the deep end to clean up well around the drain, being careful not to burn the plaster too much. 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 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.

If your pool is vinyl lined, acid is not used. Detergents, conditioners and good ‘ol elbow grease will remove the “slime”. The liner must then be “reset” with a vacuum to ensure proper fit during filling. Liner pools are normally not drained completely if it can be helped. There can be problems getting the liner to reset properly, and there is the rare danger of the walls collapsing.

It is advised that you pay a professional pool service company to perform this for you.  Contact Swemgat today for FREE advice.


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