Scottsdale Pool Acid Wash Brown and rust stains on the plaster: metal, or organic?
Stains fall into two families and telling them apart is the whole job, because neither treatment works on the other. That is why people spend a season trying products that were never going to help.
Do the test first
Vitamin C test. Crush a plain ascorbic acid tablet, hold it against the stain for about thirty seconds, look underneath.
- It lightens → metal stain. Usually iron; sometimes copper or manganese.
- Nothing → hold a chlorine tablet against it instead. If that lightens it, the stain is organic.
A minute’s work, and it is the difference between a $15 fix and a wasted summer.
Metal stains
Colours: rust brown and red (iron), blue-green to teal (copper), purple-black or brown-black (manganese).
Sources: fill and top-up water; corroding metal in the plumbing or an ageing heater, which on an older Scottsdale pool with original equipment is a real and often overlooked source; copper-based algaecides used repeatedly; and something metal left on the step.
Treatment: ascorbic acid lifts the stain from the plaster, and a sequestering agent follows to keep the metal suspended in the water instead of settling straight back onto the surface. That second step is the one people skip, and it is why the stain returns within weeks. If the source is still in the system, this becomes a routine rather than a one-off, and it is worth finding the source.
Organic stains
Colours: brown, reddish-brown or greenish, usually diffuse and often in the shape of whatever caused them.
Causes: leaves and debris left sitting, especially after a monsoon storm drops a tree’s worth of material into the water; algae allowed to root before being cleared.
Treatment: chlorine held high, plus brushing. Organic staining generally responds if the chemistry is right.
When an acid wash is genuinely the answer
Targeted treatment is right for isolated stains. An acid wash is right when the staining is widespread, has been through multiple seasons, is the shadow left by a pool that was green for a long period, or has already been treated properly and did not lift.
It works by removing the stained layer of plaster, which is also its limit, and it is only available on a plaster finish. On pebble or exposed aggregate the route is targeted stain chemistry and blasting, because acid erodes the cement matrix between the stones rather than cleaning them. The pebble finish page covers that. A pool has a finite number of washes in it, and on an older Scottsdale pool nobody knows how many are left. So spend the cheap options first, and share what you know about the pool’s history.
What it costs
| Situation | What it needs | Price |
|---|---|---|
| A few metal spots | Ascorbic acid plus sequestrant | Your chemicals |
| Organic staining, chemistry sound | Chlorine and brushing | Your chemicals |
| Widespread, into the plaster | Drain and acid wash | $400 to $800 |
| Large or heavily stained | Large acid wash | $700 to $1,200+ |
| Plaster failing as well as stained | Resurfacing prep | Quoted |
From the pricing page.
Get a quote
A deck photo, a close-up, the result of the vitamin C test, and the pool’s age. We cover Scottsdale, North Scottsdale, South Scottsdale, Paradise Valley, Fountain Hills, Cave Creek, and Tempe.
Frequently Asked Questions
How do I tell a metal stain from an organic one?
Hold a crushed vitamin C tablet against the stain for about thirty seconds. If it lightens underneath, the stain is metal, usually iron. If nothing happens, hold a chlorine tablet against it instead; if that lightens it, the stain is organic. The test costs almost nothing and decides the entire treatment.
Where does the metal come from?
Fill and top-up water, corroding metal in the plumbing or an old heater, copper-based algaecides used repeatedly, and the classic case of something metal left lying on a step. On an older pool with original equipment, corroding components are a common source.
Will an acid wash remove them?
Usually, because it removes the stained layer of plaster rather than treating the stain. That is the right answer for widespread staining. For a few isolated spots, targeted chemical treatment is far cheaper and does not spend one of the pool's limited washes.
What does it cost?
A drain and acid wash is $400 to $800 on a typical Scottsdale pool. Targeted stain treatment on a few spots is chemical work you can usually do yourself for the price of the product, and a fair pro will say so rather than sell you a wash.