Acid Washing Your Pool: When, Why, and How It's Done
A pool surface that is grey with scale, streaked with old algae stains or blotched with rust-coloured marks rarely responds to more chlorine or more brushing. That is when an acid wash comes into the conversation. It is the most effective way to bring a plaster or marbelite surface back, but it is also the most aggressive, and it is not right for every pool. This guide explains what an acid wash does, when it is worth doing, when it is not, and how the job runs from draining to refilling.
What is a pool acid wash?
An acid wash is a controlled clean of an empty pool with diluted hydrochloric acid, sold as pool acid or muriatic acid. The acid dissolves a very thin layer of the cement-based surface, and with it the scale, stains and embedded algae sitting in that layer. What is left is the cleaner, brighter surface underneath. Because a little material comes off every time, an acid wash is a restoration job, not routine maintenance.
When does a pool need an acid wash?
We recommend one when the surface has a problem that water chemistry and brushing can no longer fix. In Gauteng, the usual reasons are:
- Calcium scale across the surface, not only along the tile line. Hard municipal water and a pH left high are the usual causes.
- Algae staining that remains after the pool has been shocked, brushed and cleared — common after a pool has stood green for weeks.
- Metal stains, brown or orange, often from iron in borehole water or from corroded fittings.
- Leaf and tannin stains in the deep end, left by leaves that lay on the floor through autumn.
- A fresh start for a pool that has stood empty or neglected for months, before selling a property, or before patch repairs to the surface.
When should you not acid wash a pool?
An acid wash is for plaster, marbelite and similar cement-based finishes only.
- Fibreglass pools must not be acid washed — the acid attacks the gel coat. Draining a fibreglass pool is risky in its own right, because an empty shell can lift or distort.
- Painted pools and pebble finishes need a different approach.
- Thin, rough or flaking plaster may not have enough material left to survive another wash. There, resurfacing is the real fix, and a wash would only make the underlying problem worse.
- A scale line only at the waterline does not need the whole pool washed. Waterline tile and coping cleaning is a much smaller job, at R800.
- Stains that respond to treatment. Some metal and organic stains lift with the right chemical treatment while the pool is still full. Try that first if the rest of the surface is sound.
Why is winter the best time for an acid wash?
An acid wash needs an empty pool, and an empty pool is exposed to two risks: groundwater pressure from below, and sun on a freshly cleaned surface.
In summer, after weeks of thunderstorms, the ground around a pool can be saturated. Take away the weight of the water and the pressure underneath can lift or crack a shell. The Highveld winter is dry, so that pressure is much lower. And a freshly washed surface left empty in full summer sun can dry too fast and craze. From May to August the pool is hardly used anyway, so having it empty for a few days costs you nothing, and by September it is refilled, balanced and ready.
How is an acid wash done?
- Drain and clear. The pool is drained and the floor cleared of leaves and silt. The pump is switched off and isolated so it cannot run dry.
- Wash in sections. Diluted acid is applied to one section at a time and worked with brushes to lift the scale and stains.
- Rinse before it etches too deep. Each section is rinsed promptly. Stubborn areas get a second pass rather than a stronger mix — controlling depth is what separates a good wash from a damaging one.
- Neutralise the waste. The acidic rinse water that collects in the deep end is neutralised before it is pumped out. It must not simply be run into the garden or a stormwater drain.
- Inspect. With the pool empty, the shell, weir, light niche and fittings are checked.
- Refill and balance. The pool is refilled, and the water is tested and balanced as it fills and then watched closely for the first weeks.
Can I acid wash my own pool?
We do not recommend it. Pool acid gives off corrosive fumes and burns skin and eyes, and the work is done in the bottom of a pool shell where the air barely moves, so it needs goggles, gloves, boots and a respirator. Over-etching is permanent, the neutralised waste has to be dealt with properly, and it is easy to get the timing wrong and leave a surface exposed. If you handle pool acid for routine pH correction, always add acid to water, never water to acid, and keep it well away from chlorine.
How much does an acid wash cost?
Our pool acid wash is R3,500 for the full treatment. Refill water comes from your municipal supply, so check your municipality's water restrictions and any planned supply interruptions before you book. If you would like the surface assessed before deciding, a call-out is R650, deducted from your quote when you accept it.
We do acid washes across Centurion, Pretoria East, Pretoria and Midrand. If you want it done in winter, book early.
Should I fix anything else while the pool is empty?
Yes — an empty pool is an opportunity. Hairline cracks in the shell, a weir that has pulled away from the wall, a perished light-niche seal and weeping return fittings are all visible and within reach. If the pool has been losing water, the days it stands empty are the best time to find and fix the cause; see leak detection. For weirs, lights, valves and fittings, see pool repairs. Anything we find is quoted separately and done only with your approval, and doing it now saves draining the pool a second time.
What happens after the refill?
Fresh municipal water has little chlorine and no stabiliser, and a freshly washed surface affects the water chemistry for the first weeks. Test and balance as the pool fills, keep brushing to lift any loose residue, and do not swim until the chlorine and pH read correctly. Then keep the pH in range from the start: the same hard water and high pH that caused the scale will bring it back.
How often can a pool be acid washed?
Only as often as it genuinely needs to be. Each wash removes a little of the surface, so spacing them out preserves the finish. A pool that is kept in balance, brushed every week and never left green for long rarely needs one.
Frequently asked questions
How long is the pool out of use?
Plan on a few days. Draining, the wash itself and refilling all take time, and the refill depends on your municipal water pressure and the size of the pool.
Will an acid wash remove every stain?
It removes stains that sit in the surface layer. Deep metal stains, or damage below that layer, may lighten without disappearing, which is why we look at the surface first.
Can you acid wash a fibreglass pool?
No. Acid damages the gel coat. Fibreglass needs a different cleaning method.
Is the pool safe to swim in straight after the refill?
Not until the water has been tested and balanced. Fresh water needs chlorine, and the pH usually needs correcting after a wash.
Talk to us
WhatsApp or call Crystal Reef on 081 577 5051 with a photo of the surface, or email sales@crystalreef.co.za. For the rest of the cold-season jobs, read how to prepare your pool for winter in Gauteng.