Swimming Pool Blog

Acid Washing your Pool Safely

Acid Washing your pool Safely
by Rob Cox, March 20, 2011

Acid Washing your pool Safely

Acid washing a plastered, in ground swimming pool is a process that can be done safely by a homeowner, if proper safety precautions are taken. Three general areas of safety must be managed.

Safety regarding the discharge of the pool water, and prevent the pool shell from "popping". Safety regarding the transportation, handling and use of muriatic acid. Safety regarding the discharge of the acid wash mix after acid washing the pool.

Pumping out your pool:
If unsure about local and state regulations about draining swimming pools, contact your local building and zoning department for guidelines on swimming pool discharge. Following these pool draining techniques will get you most of the way there.

  1. Before lowering your pool water, allow chlorine levels to drop to zero and check that the pH level is within the 7.4 - 7.6 range. If you have been using algaecides or clarifiers in your pool, discontinue use and shock the pool 1 week prior and allow chlorine levels to drop to zero. The greener, the better - Having organic material in the pool water is better for pumping into green zones than pool water with high levels of chlorine or low levels of pH.
  2. In ground plaster pools after the 1960's will have hydrostatic relief plugs in the floor of the pool. These threaded pvc caps are plastered in place - usually in the center floor, 3 or more, in a line running down the main drain. There is usually another hyrdrostat inside of the main drain pot. Hydrostatic Relief Plugs will allow a build up of water or hydrostatic pressure, under the pool, to flow into the pool. If pressure becomes too great it can pop a pool shell out of the ground. Chip away the plaster surrounding the pvc cap, until you can unthread the cap with pliers. As soon as the dropping water level exposes the hydrostatic caps, start chipping away at the plaster around the cap, and remove the cap. Leave caps off until after acid washing. Replace afterwards securely.
  3. When lowering the pool water level, pump your pool water far enough away from the pool, into a storm drain, or down a gulley that is much lower than the pool itself. Consider the topography of the land around the pool, so that you don't inadvertantly pump water underneath the swimming pool.

Using Muriatic Acid:
Muriatic acid is a form of Hydrochloric Acid - very strong stuff. Acid washing a pool requires 5-25 gallons of the stuff. Careful handling of this volatile chemical is a must! Muriatic acid can be purchased at most home or hardware stores in gallons. Pool supply distributors have 5 or 15 ga. drums. Stone and masonry yards typically also sell Muriatic Acid.

  1. If transporting muriatic acid, keep it secured safely in the vehicle. Imagine what would happen in an accident and secure it accordingly.
  2. When opening and pouring muriatic acid, all persons helping should wear proper safety protection; goggles, respirators made specifically for acid gases.
  3. Acid continues to burn until sufficiently diluted. Rinse with hose quickly after pouring, and keep the hose running at all times. Use two hoses if possible.
  4. Rinse shoes and equipment before removing from pool. If skin/eye contact with acid is made, rinse thoroughly for several minutes.
  5. Always add acid to water, never add water to acid. Never allow acids to come in contact with chlorine products or algaecides.

Pumping out the Acid Bath:
After acid washing, a bubbling, noxious pool of very acidic water is in the bottom or "bowl" of the pool. This acid mix must be neutralized before pumping out to protect local watersheds and wildlife. The acid mix can be left in the pool, and balanced later, but this usually results in a ring. It's better to neutralize the acid bath mixture, pump it out, and then "pour the bowl", or acid wash the area around the main drains, neutralize again and pump out again. Then fill the pool.

  1. Use 1lb of soda ash (pH decreaser) for every gallon of muriatic acid used while acid washing the pool (assuming a hose has been running the entire time).
  2. Use a pool brush or acid brush to stir the mixture well. Keep a garden hose running into the bottom while mixing
  3. Test the acid bath mixture's pH level, to a range within 7.2-7.4. Add more soda ash if needed. Test several times to verify the reading.
  4. Use a small submersible pump to drain out the neutralized acid bath to a flat, open area, or pump to a storm drain if possible.

 For more information on how to acid wash your pool, see our acid wash page