Get the ash off the surface before it sinks, then clean the filter, test pH and alkalinity, and shock the pool. Ash is alkaline, it carries phosphates, and it eats chlorine, so your water needs rebalancing even when it looks clear again. Smoke on its own does little to the water. The ash that falls out of it does the damage.
Why does ash throw off pool water?
Burned wood and brush leave behind mineral salts that push pH and total alkalinity up. High pH makes chlorine sluggish, and the fine organic dust in the ash burns through what chlorine you have left. The ash also brings phosphates, which feed algae. Put those together and a pool can turn cloudy or start growing algae a few days after the sky clears.
Marin's worst smoke tends to come in late summer and fall, when offshore winds push it in from fires up north and east of us. Pools in Novato, San Rafael, and Fairfax sit in the warmer, drier part of the county and often catch more fallout. Fog belt pools in Mill Valley and Sausalito get damp ash that clumps and sinks faster. Either way, the same cleanup applies.
What should you do while ash is still falling?
If you have a cover, put it on. A cover holds the ash where you can sweep or rinse it off later instead of fishing it out of the water. Our post on whether you need a pool cover in Marin walks through the types.
Without a cover, skim the surface each day and empty the skimmer baskets. Ash sinks as it soaks up water, and the longer it sits on the floor, the more it works into the chemistry and the plaster.
Look after yourself, too. Health agencies advise staying indoors when air quality is unhealthy and wearing a fitted N95 mask when you clean up ash. Skip the leaf blower on the deck. It throws ash back into the air and into the pool. Ash from burned houses and cars can carry metals and other contaminants, so if a fire burned close to you, check with the county before you handle it.
How do you clean the pool once the ash stops?
Work from the top down:
- Skim the surface with a fine leaf net.
- Brush the walls and steps so settled ash moves toward the main drain.
- Vacuum the floor. If your filter has a waste setting, vacuum to waste so the fine ash leaves the pool instead of loading the filter.
- Clean the filter. Backwash a sand or DE filter, or pull and hose down cartridges. Plan on doing it more than once over the next week.
- Empty the skimmer and pump baskets again.
Keep the pump running through all of this. Circulation keeps the ash suspended where the filter can catch it.
How do you fix the chemistry after ashfall?
Test before you add anything. Expect pH and alkalinity to read high and free chlorine to read low.
- Lower pH and alkalinity with acid, in small doses, retesting between them.
- Shock the pool once pH sits back in range, since chlorine works far better there.
- Test chlorine again the next day. Ash keeps using it up for a while.
- Consider a phosphate test. If the reading comes back high, a phosphate remover can take away the algae food the ash left behind.
Cloudy water after all that usually means the filter needs another cleaning. Green water means algae got a foothold, and our green pool cleanup page covers what that takes.
Do you need to drain the pool?
Almost never. Skimming, filtering, and rebalancing recover the water in most cases, and draining wastes thousands of gallons in a county that watches its supply. Draining makes sense when debris from a burned structure has landed in the pool, or when months of ash and refills have pushed dissolved solids so high that chemicals struggle to keep up. Plaster pools can also crack or lift if someone drains them without care, so talk to a pro first.
A short list for smoke season
- Cover the pool when ash starts falling.
- Skim daily and keep the pump running.
- Vacuum to waste and clean the filter more than once.
- Test, lower pH, then shock.
- Check phosphates if algae shows up.
Our weekly service handles ash cleanup and rebalancing Monday through Friday across Marin. Call us at (415) 562-8143 or send a request.