How Many Gallons Of Muriatic Acid Will Be Needed When We Acid Wash The Pool Before We Paint It?

by YI

We are going to repaint our pool which is about 25,000 gallon and we know we need to acid wash it before we paint it.

We got a few gallon of 14.5% Hydrogen chloride Muriatic acid and we are wondering how much we need?


Thanks for the question

When you say "we" I hope you've taken into account all that is needed to do a proper acid wash, along with the safety precautions. I've done many acid washes when I took care of pools in Arizona so I'm familiar with the process.

Acid washing a pool is not like cleaning your shower. Muratic acid is very toxic, both to the skin and lungs, and should be handled with care. Long pants, rubber boots and gloves, goggles, and a breathing apparatus for each person.

You'll need to scrub the walls in 10-20 feet sections then immediately rinse each section. Don't allow the mixture to dry on the wall.

The diluted acid should be between 8% and 10% strength. Don't go over the 10% mark. Start with the walls, then do the bottom last.

Normally a 5:1 ratio is needed, 5 gallons of water to 1 acid. One gallon of diluted acid solution should cover about 100 square feet.

You should also prep the surface before doing the initial acid wash. I've used Tri-sodium Phosphate (TSP). Mix according to the directions, scrub in 10 - 20 foot sections, and rinse.

Without knowing the shape of the pool, only the gallons, it's a bit difficult to give you the right square footage. This is the formula you'll need to calculate it.

You need to add up the floor and wall surfaces to get total area.

Next, you need to know the length, width, and average depth of the pool. Be sure to measure the longest length and width.

This is all in square feet and for a rectangle pool.

  • Length X Width to calculate the floor area

  • Length X Average Depth X 2 to calculate the long walls area

  • Width X Average Depth X 2 to calculate the short walls area

    Add all of these to get the get total square footage.

    If your pool is free-form or an irregular shape, you'll need to multiply your total square footage by 0.9. This takes into account any steps, sloping, or lost area.

    Here's an example:

    Your pool is 30 feet long and 20 feet wide. Shallow end is 3 ft. and deep end is 9 ft. Average depth is 6 ft. 9 + 3 divided by 2 = 6

  • L (30) X W (20) = 600 - Floor area

  • L (30) X average depth (6) X 2 = 360 for the long wall area

  • W (20) X average depth (6) X 2 = 240 for the short walls

    Total everything up:

    600 + 360 + 240 = 870 square feet. Let's round it to 900.

    At a 5:1 ratio you'll have a total of 6 gallons of acid/water solution. To cover 900 square feet you'll need about 9 gallons of solution.

    To be on the safe side you might consider buying a couple extra gallons. If you don't use them for the acid wash, you'll probably use them for lowering the pH and alkalinity.

    To post a reply, or if you have a similar question, you can see your post on the Q&A page in the "Pool Paint" category.

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    Hope this helps and good luck with the acid wash.


  • Comments for How Many Gallons Of Muriatic Acid Will Be Needed When We Acid Wash The Pool Before We Paint It?

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    Jul 25, 2013
    Amounts for Acid Wash
    by: Anonymous

    Is the amount of water acid solution for 900 square foot pool correct? one gallon of solution covers 100 sqft. at 900 sqft it seems like it should be 9 gals. 7.5 gal water and 1.5 gal acid. Or am I just not seeing something?

    Thanks for the comment

    Yes you're right. I multiplied when I should have divided. I made the correction in the post.


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