Pool Plaster Stains
Stain colour tells you what caused it, and the cause determines whether a chemical treatment will lift it or whether you are looking at resurfacing. The vitamin C test settles most cases in about a minute.
Is it urgent?
No. Staining is cosmetic and a stained pool is perfectly safe to swim in. It is worth acting reasonably promptly for one reason only: fresh stains on a sound finish lift far more easily than old ones that have penetrated a surface which has since become porous.
Identify it by colour
| Colour | Likely cause | Typically removable? |
|---|---|---|
| Rust brown / orange | Iron | Yes — ascorbic acid treatment |
| Blue-green / teal | Copper, often from an ionizer or algaecide | Yes — ascorbic acid treatment |
| Black / purple-black | Manganese, or black algae | Usually — depends which |
| Green-brown, blotchy | Organic: leaves, algae, berries | Yes — chlorine and brushing |
| Grey-white crust | Calcium scale | Yes — acid wash or bead blasting |
| Grey / mottled, cannot be lifted | Aggregate exposure, not a stain | No — the finish is worn through |
| Uniform dinginess across the pool | A porous, aged finish | No — resurfacing |
Two tests you can safely do
Both take a minute and are the standard way of narrowing this down before spending anything.
- The vitamin C test — for metal stains. Hold a crushed vitamin C (ascorbic acid) tablet against the stain for about 30 seconds. If the stain lightens or disappears, it is a metal stain — iron or copper — and will respond to an ascorbic acid treatment.
- The chlorine test — for organic stains. Hold a chlorine tablet against the stain briefly. If it lightens, the stain is organic and will respond to shocking and brushing. Do not leave the tablet resting on the surface, which can bleach a spot.
- Neither works?. If neither test shifts it, you are probably looking at exposed aggregate or a worn finish rather than a stain — which is a resurfacing conversation.
What not to do
- Do not reach for acid first. An acid wash removes a layer of the finish. It is the right answer for scale and the wrong answer for a metal stain that would lift with ascorbic acid for a fraction of the cost.
- Do not add metal sequestrant without identifying the source. If iron is entering with fill water or from a corroding heater, sequestrant treats the symptom while the source keeps supplying more.
- Do not mix pool chemicals. Particularly acid and chlorine products. Follow label instructions and add chemicals separately.
- Do not drain the pool to "have a look". A drained shell can be damaged by groundwater pressure and by UV drying. Draining is a contractor decision.
What each fix costs
| Treatment | Cost | For |
|---|---|---|
| Ascorbic acid treatment | $80–$250 (DIY chemicals) | Iron and copper stains |
| Shock and brush | $40–$120 (DIY chemicals) | Organic staining |
| Professional stain treatment | $300–$700 | Where DIY has not worked |
| Acid wash | $450–$1,100 | Calcium scale and general dinginess |
| Bead blasting | $800–$2,000 | Heavy scale on a sound finish |
| Resurfacing | $8,500–$22,000 | Staining has penetrated a porous, aged finish |
When staining means the finish is done
There is a point where staining stops being a water-chemistry problem and starts being a surface-condition one, and it is worth recognising rather than spending repeatedly on treatments.
- Stains return within weeks of a successful treatment.
- Neither the vitamin C nor the chlorine test shifts the discolouration at all.
- The surface is also rough — a porous finish absorbs stains rather than holding them on the surface.
- The pool has already had two or more acid washes.
- The discolouration is uniform across the whole pool rather than patchy.
How to read a PoolSavr estimate
- Step 1
Instant estimate
Based on your project selections and general pricing assumptions. Useful for deciding whether a project is realistic.
- Step 2
Measured estimate
Uses your pool, spa, or deck dimensions to price the work against the areas actually being resurfaced, tiled, or replaced.
- Step 3
Contractor proposal
Prepared by a licensed professional after inspecting the site. This is the only number that becomes a contract.
PoolSavr is an estimating and matching platform. We do not perform pool work ourselves — licensed local professionals do. Contractors pay PoolSavr for qualified project leads, which is how the estimating tools stay free for homeowners. A PoolSavr estimate is a planning range, never a guaranteed quote — read thefull estimate disclaimer.
Frequently asked questions
- How do I identify what is staining my pool?
- Start with colour: rust brown suggests iron, blue-green suggests copper, green-brown suggests organics, grey-white crust is calcium scale. Then confirm with the vitamin C test for metals and the chlorine test for organics — whichever lightens the stain identifies it.
- Will an acid wash remove my pool stains?
- It will remove calcium scale and general surface dinginess, and it will lighten most things by removing a thin layer of the finish. That is also its cost — a pool can only take two or three acid washes in its life. For metal stains, ascorbic acid treatment is cheaper and does not consume the finish.
- Why do my pool stains keep coming back?
- Because the source is still there. Metal stains recur if iron or copper keeps entering through fill water, a corroding heater, or a copper-based algaecide. Organic stains recur if debris keeps sitting on the surface. Treating the stain without removing the source is a repeating cost.
- Are pool stains harmful?
- No. Staining is cosmetic and a stained pool is safe to swim in. The concern is what it can indicate — persistent metal staining may point at a corroding heater or plumbing component worth investigating.
- Can stained plaster be restored, or does the pool need resurfacing?
- It depends on whether the stain sits on the surface or in it. Fresh stains on a sound finish usually lift with the right treatment. Once a finish has become porous with age, staining penetrates and no treatment reaches it — that is when resurfacing becomes the answer.
Ready to see what your project costs?
Start with the work you are considering. You will get a preliminary range before anyone asks for your phone number, and you decide whether to request a contractor review at the end.