How to Drain and Acid Wash a Pool (Safely)
By Pool DIY Pro TeamJanuary 27, 2025No CommentsMaintenance
Most pool problems are solved with sweat and chemistry. But occasionally, a pool is too far gone: an inherited pool that sat stagnant, a bad winterization that left a green, slimy mess, or years of stains and mineral buildup no chemical will lift. In those cases, a full drain and acid wash is the reset.
This is a serious, mostly-once procedure, not routine maintenance. Done carefully it strips stains and buildup and gives you a fresh surface. Done carelessly it can permanently damage your pool. Read the warning below before you start.
Read This First: The Structural Warning
Draining ALL the water from a gunite, concrete, or hard-sided pool can cause catastrophic structural failure or serious surface damage. Many stone pool structures rely on the weight of the water to hold them in place; empty, they can crack, heave, or "pop" out of the ground from hydrostatic pressure.
- Do not fully drain a pool on a whim, it is a last resort for serious problems only.
- If you're unsure about your pool type or water table, hire a professional. This is one job where the risk often outweighs the DIY savings.
- Never attempt this without proper protective gear: long sleeves, long pants, boots, gloves, and eye protection. You'll be handling muriatic acid.
When a Drain and Acid Wash Is Actually Needed
A "drain and clean" is technically an acid wash plus the removal of a thin layer of surface plaster. It's highly effective, but only warranted when milder options have failed.
- Deep, set-in stains or years of algae buildup that shocking and brushing won't remove.
- Heavy mineral scale coating the surface.
- An inherited or long-neglected pool that has turned into a stagnant, black-water lagoon.
- NOT for: routine cleaning, a temporary algae bloom, or normal seasonal upkeep, those are chemical fixes.
Step-by-Step: The Drain and Acid Wash Process
Work in small sections, keep surfaces wet until you're ready for them, and never let acid sit on the plaster. Plan for the whole process to take a few days.
- Drain the pool using its built-in drain or a submersible pump. This typically takes a day or two.
- As it drains, scrub the walls and surfaces to break off buildup and residue, hosing them down periodically so debris doesn't bake on.
- Let the empty pool surface dry completely before applying acid, mixing acid with standing water is dangerous.
- Mix the muriatic acid per the label (use the weakest effective solution) and apply with a chemical sprayer, starting at the deep end near the drain.
- Apply to a small section, then rinse it quickly. Never let acid dwell on the plaster. Work section by section around the pool.
- Neutralize the acidic water pooling at the bottom with soda ash until a pH test kit reads about 7.2.
- Pump out the neutralized waste water and rinse the whole pool thoroughly, possibly a couple of times.
- Refill with fresh water (two garden hoses speed it up), balance the chemistry, and shock with chlorine. Let it stabilize a day or two before swimming.
Supplies You'll Need
- Muriatic acid (or a dry acid alternative) and a chemical sprayer
- Soda ash to neutralize the waste water
- A submersible pump (unless using the built-in drain)
- A pH test kit to confirm neutralization before pumping out
- Full PPE: goggles, acid-resistant gloves, boots, long sleeves and pants
Best Products
Disclaimer: all product links below go to Amazon.com. As an Amazon Associate we may earn from qualifying purchases.
1Best Submersible Drain Pump
Submersible Utility / Pool Drain Pump
A submersible pump drains the pool faster and more controllably than the built-in drain, and doubles as a cover pump. Look for a high gallons-per-hour rating and a standard garden-hose outlet.
Pros
- Faster, more controllable draining
- Reusable for cover water and floods
- Simple hose connection
Cons
- Adds upfront cost vs. built-in drain
- Needs a nearby outlet and safe discharge point
2Best Acid Applicator
Chemical / Acid Sprayer
An acid-resistant pump sprayer lets you apply diluted muriatic acid evenly to small sections, which is exactly how a safe acid wash is done. Do not use a general-purpose sprayer with metal parts.
Pros
- Even application on small sections
- Acid-resistant seals and wand
- Far safer than pouring
Cons
- Must be rinsed and stored carefully
- Acid-rated models cost more
3Best pH Test Kit for Neutralizing
Pool pH / Water Test Kit
You must confirm the waste water is neutralized (around pH 7.2) before pumping it out. A reliable test kit is essential for this step and for balancing the refill.
Pros
- Confirms safe pH before discharge
- Reused for ongoing water balancing
- Inexpensive and quick
Cons
- Reagents expire over time
- Liquid kits take a little practice to read
Frequently Asked Questions
Can I acid wash without fully draining?
There are no-drain acid treatments for mild cases, but a true acid wash that removes surface plaster requires an empty pool. Given the structural risks of draining, try no-drain and chemical options first.
How often should a pool be acid washed?
Rarely, often just once every several years, or when you inherit a badly neglected pool. It removes a thin layer of plaster each time, so overdoing it shortens your surface's life.
Is this a DIY job or should I hire a pro?
It can be DIY with great care and full PPE, but the draining step carries real structural risk and you're working with hazardous acid. If you have any doubt about your pool type or the water table, hire a professional.
Final Verdict
A drain and acid wash is a powerful reset for a stained or neglected pool, but it's a last resort, not routine care. Respect the structural warning about draining hard-sided pools, work in small rinsed sections, neutralize before you pump out, and gear up properly. If anything feels beyond your comfort level, this is a smart job to hand to a professional.