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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    Check back to this post for updates or answers.

    Hope this helps and good luck with the acid wash.


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    Milky/Chalky Residue In Pool

    by Adam

    I painted my pool with epoxy paint 4 years ago. It's a concrete pool with plaster so I painted over the plaster of course. It's really milky color and when I sweep it, there's chalk that come off and makes the pool very hazy and milky.

    Is there a way I can fix this problem without having to paint the pool? I've been told that I can't paint the pool now, because it's too hot. I'm at a loss. Please help. Thank you

    Hi Adam. Paint is only as good as the prepped surface. If the surface was not properly prepared, the paint will eventually start to come off, or blister. Not knowing the details of the prepped surface, I can only go on assumptions.

    If the paint is coming off due to a poor working surface, the best and long term solution is to rework the surface properly and repaint. I'm not aware of any chemical that can lessen the affects of paint loosing up and coming off.

    Some epoxy paints have changed the formulation to be more environmentally friendly. I've been receiving many comments and questions about this over the last 2 years, compared to previous years. After doing some digging I found that some paints have changed. This is the only conclusion I could come up with.

    Some manufacturers removed the good solvents in the paint in an effort to reduce the amount of volatile organic solvents (VOCs) released during the drying/curing process.

    If a paint says "Low VOCs" or "VOC compliant", there's your indication that the paint formula has been changed.

    It could be a combination of the surface + epoxy paint that is causing the issue. A lower CH level can also contribute to this issue. Maintain the CH at 150 - 250 ppm. If you already have hard water, >250 ppm then there's no need to add calcium chloride to increase it.

    Other than constant filtering and brushing in an attempt to clear the water, to the best of my knowledge, the surface would need to be reworked and painted.


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