Mustard algae is stubborn but beatable with shock and persistence.

It’s a pain, but yes, you can get rid of it — just don’t expect a single chlorine tablet to do the job.

Mustard algae (yellow algae) looks like pollen or dirt on the walls and floor. It’s chlorine-resistant, so normal maintenance levels won’t touch it. The key is breaking its lifecycle with a brutal combination of high chlorine, thorough brushing, and no shortcuts.

Here’s the plan: brush every surface — walls, floor, ladder, skimmer, filter — because the algae clings tight. Then shock the pool to 20-30 ppm of free chlorine (not combined). Keep it there for 24-48 hours if you can. Run the pump nonstop. Brush again every day. If it comes back, add an algaecide specifically labeled for yellow/mustard algae. Some people also use a phosphate remover if it’s a recurring issue.

The mistake most people make is under-shocking or not brushing enough. Mustard algae laughs at a standard shock level. You have to go nuclear and stay on top of it for a few days.

Your filter will hate you — that’s normal. Backwash or clean it often. And if you have a pool cover, wash that too, because algae can hide there.

You will beat it, but you have to be more stubborn than the algae.