Wildfire Ash in Your Pool: What to Do, in Order

The fire season here runs from the first dry Santa Ana winds in September through to the rains, and a pool does not have to be anywhere near the flames to be affected. Ash travels tens of miles on those winds, and it is fine enough to pass straight through a skimmer basket and settle on the floor.

What follows is what our technicians do, in the order they do it. None of it is urgent in the first hours — but the longer ash sits in the water, the more of it dissolves, and dissolved ash is a chemistry problem rather than a cleaning one.

While Ash Is Still Falling

Do not start cleaning in smoke. Ash that is airborne is what you should not be breathing, and the pool will still be there tomorrow. If you have to be outside, an N95 is the minimum.

• Leave the pump running. Circulation keeps chlorine moving through water that is being loaded with organic material. A still pool under falling ash is how a green one starts.
• Empty the baskets daily, not weekly. They fill with grey sludge faster than you would expect, and a blocked skimmer starves the pump.
• Watch the filter pressure. Eight to ten psi above clean means it needs rinsing or backwashing, and during a fire that can happen in a day.
• Do not put a mesh or floating cover on. It collects ash, sags and drops the whole load into the water at once. A solid safety cover is the only kind worth using here.
• Keep the level up. Hot, dry, windy days drop it fast, and a pool running below the skimmer throat pulls air into the pump.

Once the Air Clears, Work in This Order

1. Skim the surface with cloth over the net. An old t-shirt stretched over the net frame catches the fine film that a bare mesh net drives straight through. This one trick removes more ash than anything else you will do.
2. Empty both baskets. Skimmer and pump. Then check them again an hour later.
3. Brush the walls and floor, then wait. Brushing lifts the settled layer so the filter can see it. Give it a few hours to fall back to the floor before the next step.
4. Vacuum to waste, not through the filter. Ash is fine enough to pass through a filter and come back into the pool. Set the valve to waste and accept the water loss — this is the step people skip and then wonder why the water stays grey.
5. Test, and expect the pH to be high. Wood ash is alkaline. Bring alkalinity to 80–120 ppm first, then pH to 7.4–7.6, in that order.
6. Clean the filter properly. Not a rinse. Cartridges come apart and get washed pleat by pleat; DE grids get stripped and recharged. After a heavy ash fall a cartridge sometimes does not come back and has to be replaced.
7. Shock at dusk. About 2 lb of cal-hypo per 10,000 gallons after a serious ash load. Sunlight burns off shock added during the day.
8. Run the pump 24 hours, then check the pressure again. Expect to clean the filter a second time within the week.

Fire Retardant Is a Different Problem

If aircraft dropped retardant anywhere near your street, you may find a pink or rust-coloured residue on the deck and in the water. That material is ammonium phosphate — agricultural fertiliser, in effect.

Phosphate is algae food, and chlorine does nothing to it. A pool that has taken retardant needs a phosphate test, a phosphate remover and a filter clean afterwards, because the remover works by binding the phosphate into something the filter can catch. Shocking it harder instead is money into the water.

What Ash Does to the Chemistry

Wood ash is alkaline, so a heavy fall pushes both pH and total alkalinity up. High pH makes chlorine lazy: the same reading on the test strip does far less sanitising at 8.0 than it does at 7.5. Meanwhile the organic fraction of the ash consumes chlorine outright and adds phosphate on the way.

That combination — chlorine being eaten, chlorine that remains working at half strength, and fresh algae food in the water — is why pools go green after a fire rather than during it. If yours already has, that is a different job and cleaning the ash out first is part of it.

In the foothills this happens at a lower level all year round, fire or no fire — wind-borne ash and grit are the standing problem on our Altadena service pages for a reason. And when the first rain finally arrives, it washes everything that has been sitting on the roofs and hillsides into the pool at once, which is its own clean-up.

When Cleaning Is Not Enough

Occasionally the water is past saving: phosphate that will not come down, alkalinity that cannot be corrected without dumping acid in by the gallon, or a pool that took burnt debris rather than ash. Then it is a partial drain and refill rather than a clean.

• Partial, not complete. An empty shell can float out of the ground or crack when the groundwater is high, and plaster that dries out is finished. Draining a pool to the bottom is a job with pressure relief and a plan, not a garden hose left running.
• Not into the street. Storm drains in Los Angeles County run to the ocean untreated, and chlorinated water in them is an offence in most cities we work in. Dechlorinated water goes through a sanitary sewer clean-out on the property — the same route as backwash.
• Replace a third to a half, then rebalance. That is usually enough to bring the numbers back into range without emptying the shell.

If the Fire Came Close

A pool that was near the fire line needs the equipment checked before anything is switched on. Heat warps and melts plastic — pump housings, valve bodies, cartridge housings — and a heat-damaged pump run dry finishes itself in minutes. Look at the pad before you look at the water.

Pools are also a water source during a fire, and crews and aircraft do draw from them. If yours was used, the level will be down, the pump may have run dry, and there may be debris in the water that was never airborne. That is a repair visit before it is a cleaning one — diagnosis is $0 in our service area.

Do Not Swim Until It Is Right

Grey, hazy water after a fire is not just unpleasant to look at. Chlorine that cannot hold a reading means the water is not being sanitised at all, and burnt material carries things nobody should be swimming in. The rule we give clients: clear enough to see the main drain, chlorine holding a stable 1–3 ppm for 24 hours, pH back in range. Until all three are true, keep everyone out.

When to Call Someone

Through fire season the calls follow a pattern: water still grey after the third clean, a filter that will not come back, chlorine that vanishes overnight, or a pump that has been through something. Any of those is past the point where more chemicals help.

Send us a photo of the water or call (818) 740-6099. A storm or fire clean-up is a fixed price once we have seen what is in the pool, and current prices are worth confirming by phone — the price list is a guide, not a quotation.