How To Acid Wash a Pool

Empty Pool

Acid washing isn’t always a necessary step to take to get your pool clean. However, it may be necessary for some pool owners who lament the fact that their pool doesn’t look quite like it used to. If your pool is stained or has turned into a “black lagoon,” either because of an algae problem or because your pool wasn’t properly winterized, it might be time to acid wash the pool.

Determining Need

Lots of things can alter the color of your pool: algae, leaves, calcium buildup, and rust are just a few causes. Pool acid washing actually etches off a tiny layer of plaster, exposing the fresh plaster underneath. It’s something you should NOT do every year, otherwise your pool will need to be replastered after a few treatments. It’s more of a last-ditch effort to clean up a pool that may have experienced years of staining and should only be done every few years.

A good rule of thumb for deciding whether or not you need to acid wash a pool is to check and see if you can see the bottom of the pool. If you can, it can usually be brought back to normalcy with chemicals, filtering, and a little elbow grease. If the floor isn’t visible, the cost of chemicals and labor is generally greater than the cost of a drain and acid wash, plus takes much longer to return to usable conditions.

Extensive algae blooms are a major cause of plaster staining and if they’ve been clinging to your pool walls all winter, an acid wash may be necessary. If your pool has had an algae problem for years, changing the water and acid washing the surfaces that algae is prone to stick to is likely to give your water a much needed lift.

  • Acid is a dangerous and corrosive substance. If you’re not comfortable taking the time to properly mix and apply the acid, it may be best to ask your local pool professional to undertake the job instead.
  • If you DO want to save the money by acid washing your pool on your own, make sure you’re careful and wear all the necessary safety equipment. It also never hurts to have a buddy help/supervise or readily available in case of an emergency.
  • Before you get started, make sure you check local city codes to be sure you are pumping out the excess water/waste to a safe location. You may also want to see what your local waste water regulations are.
  • Keep pets and children away from the pool area while acid washing is taking place. You don’t want to run the risk of anyone coming in contact with the acid solution.
  • Your protective gear is very important and should be donned before you get started cleaning your plaster. You’ll want to wear gloves, a jumpsuit or protective clothing, rubber boots, a breathing mask designed for acid fumes, and goggles.

Getting Started:

Before you start to drain the water, turn off the power and the pool’s filtration system and close the fill valve. As you drain the pool, wash down the sides with water as the pump runs and remove the algae and the leaves. If your pool has an autofill feature, make sure that you turn that off as you drain it. Bag up all of the gunk that collects on the bottom of your pool and remove. When the pool is clean of any extra slime and the bottom is empty, you can start to acid wash the plaster.

Mixing Acid

To etch off this tiny layer of plaster, you’ll need help from muriatic acid—a substance that is available at most hardware or paint specialty stores. Acid is dangerous so make sure you pay close attention during its application.

Add 1 gallon of muriatic acid to 1 gallon of water in a watering can (preferably metal) by adding the acid to water already in the can and not the other way around. NEVER add water to the acid as this can cause a bubbling reaction that could spray onto you or your surroundings.

Scrubbing the Walls

Wet a 10 foot section of your pool wall with a hose (keep the hose running), then have someone pour the acid mixture down the wall, from top to bottom, using a long pool brush (preferably one meant specifically for this task) to scrub the wall. Don’t let the acid sit on the surface for much longer than 30 seconds at a time. Brush over the surface to move the acid around before rinsing thoroughly. Make sure the acid is completely rinsed off because otherwise, it’ll continue to etch the plaster.
  • If the mix doesn’t seem to be doing its job, you can either increase the strength (acid to water ratio) or let it sit on the plaster longer. Just watch carefully and don’t increase either increment too dramatically without testing on a small portion of floor or wall. You can also buy an additive that will thicken the acid and help it to stick on sides and stairs longer.

While you’re working your way around the pool, try to prevent the acid from wearing a channel path from shallow end to deep end to avoid a worn stripe on floor.

Neutralize the Excess

After you’ve washed the sides and bottom, you’ll have a puddle at the bottom of the pool that is foamy. This needs to be neutralized before it gets pumped out. Use 2 pounds of soda ash per 1 gallon of acid used on the plaster. Spread the ash over the puddle while stirring with a pool brush. The acid is properly neutralized when the mixture stops bubbling and foaming.

Use a small sump pump to pump out the remaining water at the deepest part of the pool. Even if properly neutralized, the water may destroy plants or kill fish so don’t dump it in your water beds or in a stock pond. Pump it into your sewer clean-out valve and continue to rinse the pool as it drains.

Clean the Bowl

Rinse the plaster thoroughly with your garden house, working your way around the sides. Scrub and spray as you go until the entire pool is clean. Rinse out the bottom of the bowl after the water is drained. Pour water over any remaining acidic residue, cleaning up carefully around the pool drain.

If your pool is still stained or dirty, you may repeat the process again, being careful not to burn off too much plaster.

Extra Safety Tips
  • Don’t rush the job! You want to work quickly but you also want to be safe while you do it. Don’t hurry through the process to the extent that you become negligent of your surroundings.
  • Muriatic acid fumes can be strong and dangerous if not adequately protected. Don’t underestimate it! Make sure to wear a respirator that will block the fumes along with your other safety equipment.
  • Spray yourself off before exiting the pool—transferring the acid from outside to your house can be hazardous.
  • If any acid gets in your eyes or mouth, rinse with the house for 15 minutes without a nozzle on. Acid on the skin usually won’t burn too much—just rinse thoroughly for 30 seconds-1 minute.
Bromine: Pool Sanitizer FAQs

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