Difficulty: 2 Ducks (Out of 4)

Time: 3 days total, but only one day for acid washing (~4 hours). Day 1 is draining, Day 2 is acid washing, Day 3 is refilling and chemical balancing

The Fine Print: These chemicals are very caustic and dangerous. Always use proper precautions. It’s also easy to stain or streak the surface of your pool by unevenly applying acid. When in doubt, start with a more dilute acid solution and re-apply as needed. Always add acid to water! Wear a respirator! All pools are different and what we say here may not apply to yours!

Why and When to Acid Wash

We go over what an acid wash is, why you might want one, and when you should (and shouldn’t) do it, here. You’re reading a guide about how to acid wash, so we assume your mind is made up already, but as a refresher, here are the “do nots”:

• Do not acid wash in the Summer (in Arizona at least). Pool surface (plaster in particular) can become damaged or crack when dry and exposed to heat. Acid washing requires draining your pool. A general rule of thumb is that if the temperatures exceed 90 degrees for a large portion of the day, do not drain your pool.
• Do not acid wash too often. Acid washes etch away a small portion of your pool surface. Repeating this process too often can eventually wear away entire portions of the surface of your pool. If you see any rebar or other portions of the foundation, you cannot acid wash your pool. You must, at a minimum, patch, although the best solution would be to resurface
• Do not spot acid wash. If only one part of your pool is stained, you should still acid wash the entire pool. Spot acid washing will lead to a very noticeable color difference

Getting Started

Preparation is important. Acid cannot remain on the surface of your pool for very long, so once you start the acid wash process, it needs to run straight through until you finish it. That means it’s very important that all equipment is ready before any acid is poured. Let’s get going!

Personal Gear

Muriatic acid is nasty. You can always find someone barefoot with no respirator on YouTube, but we like to live life in a lower gear than them. We think anyone in the pool itself should be wearing the following:

• Respirator
• Goggles
• Long-Sleeve Shirt
• Long Pants
• Rubber Boots
• Rubber Gloves

Equipment

(We’re not a Leslie’s shill nor do we make any money from them - links are just for reference so you understand what equipment we’re talking about)

Required

• Sump pump
• Backwash or vacuum hose (sufficiently long to run from sump pump to sewer drain)
• Muriatic acid (~8 gallons, but it depends on the dilution ratio, which depends on the level of staining)
• Watering cans (1 is okay but 2 or 3 make it easier), 2-gallon
• Soda ash (2 pounds per 1 gallon acid used)
• Garden hose sprayer head
• Deck brush, with broomstick handle
• Chemical test kit / strips

Optional But Helpful

• White-N-Brite from Bio-Dex, this is an additive that thickens the acid-water solution to help eliminate streaks. It also reduces fuming of the acid. Not necessary but highly recommended. 8oz per 3 gallon solution assuming 2:1 water to acid ratio, so 1-2 quarts (you can go lighter than 8oz and still achieve effectively the same effect)
• Stirring stick, like home depot paint sticks, extra PVC pipe, etc., for stirring together acid-water-BioDex solution
• Painters tape, to visually section off the pool, and to section off your watering cans to ensure accurate dilution ratios
• Tarp, to set watering cans on while mixing
• Pressure Washer, very optional. We pressure wash the surface of the pool after draining but before acid washing. This helps us see what is truly a stain vs. debris. If you don’t have one, just spray the walls of the pool with your hose
• Hose Auto Leveler Attachment, very optional. If you cannot be home while your pool is refilling, the auto-leveler will shut off your garden hose when the pool is nearly full

Help

Because of the application-brush-rinse process, this is a 2-person job. Three people can be even more helpful. We strongly discourage anyone from trying this on their own - you have to do too much too quickly. Here’s how we recommend dividing roles:

• Brush Guy: One person in the pool, with a deck brush, scrubbing the acid solution into the surface of the pool
• Acid & Rinse Guy: One person on the pool decking, pouring the acid solution with the watering can, and then rinsing the solution off with water after Brush Guy finishes brushing

Day 1: Draining the Pool

This is the easiest part. Do this:

1. Shut off the pool sub-panel at the breaker
2. Turn off any water supply to the auto-fill (if present)
3. Attach drain hose to the sump pump
4. Lower the sump pump into the deepest part of the deep end of the pool
5. Run the drain hose to the sewer line
6. Plug in the sump pump

Make sure your sump pump has an auto-off feature so the pump doesn’t run dry. We’d also recommend cleaning your filters if you have cartridge or DE filters

Day 2: Acid Wash

The fun begins!

Prepare for Acid Wash

1. Unplug sump pump (but leave the drain hose connected and running to sewer line) - the reason to unplug is you don’t want it to kick back on while acid washing. You want to ensure the mixture is fully neutralized before pumping away
2. Spray down the walls with a pressure washer. If using a garden hose attachment instead of a pressure washer, spray down the walls and then brush with your pool brush to remove as much debris as possible
3. Section off the pool into 6 even sections. Mark these sections with a piece of painters tape on the pool decking. The reason for doing this is it helps ensure even distribution of acid around the pool and gives you a good cadence for rinsing.
4. For Brush Guy: put on all safety gear, grab deck brush, and enter the pool. It’s important to note that Brush Guy should now not leave the pool unless his boots are thoroughly rinsed (i.e., until you are done acid washing). Once his / her boots get acid on them, they can stain pool decking, brick, carpet, etc. and so they should remain in the pool until they can be thoroughly rinsed
5. For Acid & Rinse Guy: Put on respirator and gloves. Lay down tarp and mix the acid solution. The dilution depends on how stained the pool is, but more dilution is generally better. We like more dilute but 2 applications, rather than more concentrated but 1 application. It’s more forgiving this way. We’d recommend 1 gallon acid to 3 gallons water, with 2 applications. If using this 1:3 ratio, mark off your watering cans into thirds using painters tape, so that you can approximate the right ratios. Fill the watering cans three-fourths up with water, and then fill the remainder with acid. Always add acid to water, never water to acid. Add a few ounces of Bio-Dex solution (a third to half a cup) and stir with stirring stick
6. There will be some residual water at the deep end of the pool, from the water that the pump didn’t get and the water from rinsing the walls of the pool. Add 2 pounds of soda ash to this water. This will neutralize the acid as it drains, keeping that pooled water from turning acidic and staining the deep end of the pool
7. Check to make sure water is running to your garden hose, and that your garden hose can reach all the way around the pool, so that you will not be stuck short anywhere

Acid Wash

1. Acid & Rinse Guy: Starting with a section in the deep end, pour the acid solution, starting at the tile line. Pour the entire 2-gallon watering can, attempting to evenly coat the entire section
2. Brush Guy: Scrub the entire surface of the section, to evenly coat. Scrub horizontally more than vertically, to help avoid any streaking
3. Acid & Rinse Guy: As soon as Brush Guy is finished brushing, rinse fully and thoroughly with water. Once finished rinsing, add ~1 pound of soda ash to the water at the bottom of the pool. Tip: If the section includes a flat surface, like a step or a bench, spend extra time rinsing. Any acid that is not rinsed will sit and continue to etch into the surface, rather than draining down, leading to staining
4. Continue section by section around the pool until first application is complete
5. The only portion of the pool that was not washed and scrubbed during this application should be the very bottom of the deep end, where water pooled. Use a test strip to test pH and ensure it is approximately neutral, adding soda ash as needed. Drain off this pool of water and move the sump pump out of the way. Use a watering can to coat the deep end of the pool where you were not able to apply solution to previously. Brush and rinse. Neutralize the new pool of water with 1 pound soda ash
6. Repeat the same process for a second application
7. Test pool of water again and balance with soda ash as needed to ensure neutrality. Brush Guy should slosh around in water to thoroughly rinse boots. Pump out resulting water
8. Thoroughly rinse the entire pool surface one more time with water, rinse boots again, and pump out resulting water

Refill Pool

1. Remove sump pump and disassemble drain hose
2. Place garden hose(s) inside pool and begin refilling. If using a garden hose auto leveler attachment, attach it now. Note: Do not turn any built-in auto-fill back on yet. It should only be turned on when the pool is within a foot or less of target water level
3. If not using a garden hose auto leveler attachment, set a reminder on your phone for every ~3 hours to check water levels. Once the pool is within ~2 feet of being full, set reminders for every 1 hour. Turn off the hose when your pool is full
4. If using a built-in auto-leveler, turn water supply back on
5. Turn on pool sub-panel breaker. Note: You will likely need to reset your pump timer
6. Balance chemicals. You can use a pool start-up kit, although we think that a lot of these chemicals are unnecessary for clean tap water (e.g., algaecide). That said, make sure you add chlorine or salt (for salt cell pools)

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