The term “acid wash” is used to describe a process of using a mixture of water and muriatic (hydrochloric) acid to remove tough stains from plaster pools.

Occasionally, a pool has been left neglected for a period of time, or perhaps winterizing the pool was performed improperly, and significant buildup of algae and hard water has led to tough stains on the porous plaster of your pool. The water may become murky and very dark green or black. Often, once it reaches this state, normal cleaning and scrubbing are no longer enough to return the pool to a healthy and appealing state. A general rule of thumb to follow is if you can’t see the bottom, you’ll benefit from an acid wash.

Other reasons you may need an acid wash include calcium deposits, chlorine or other stains, or rapid regrowth of algae after scrubbing which can indicate that the algae spores are embedded deep within the plaster of the pool, even if there are no other visible signs.

Acid washing, also often referred to as a “drain and clean,” is an intense process that will essentially strip away a thin layer of plaster, leaving a fresh like-new layer of plaster behind. Because the process can potentially damage your pool if used too frequently, it is advised to be performed roughly only once every 5 to 7 years. While it is possible to perform the acid wash yourself, it is strongly discouraged. Acid can cause serious injury in the form of burns and respiratory damage if used without the proper protective gear and breathing apparatus. Additionally, if used incorrectly or allowed to sit for too long, damage or discoloration of the plaster can occur. Acidic water must also be neutralized with soda ash for environmental safety. Due to the dangerous nature of the harsh chemicals, it is a process best left to the professionals.

The process will take several hours, depending on the size of the pool, and the pool will need to be entirely drained, cleaned and then refilled. Costs will vary according to your location, the size of the pool, and the degree to which your pool is stained. While many handymen offer this service, it is often more expensive than going through your local pool company – they already have the necessary supplies and experience. A reputable pool company will provide you with a free quote. Be wary of someone who advises re-plastering the pool instead of acid washing. While both options will achieve a similarly refreshed appearance, re-plastering is considerably more expensive, and is probably only necessary if your pool is showing other signs of damage, such as a rough or sharp surface or thinning of the plaster.

Remember, the best option for your comfort and safety, as well as your budget, is preventative and routine maintenance to keep your pool in optimal condition!