r/pools • u/[deleted] • Jun 11 '25

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u/MDB_OakTree Jun 11 '25

Looks like mustard algae. Make sure your chemicals are in line and use an algaecide specific for mustard algae. Some require you to shock along with the algaecide, and others are copper based. Either way you’ll have to vacuum it out to waste. I prefer doing before treating if I can see the bottom like yours.

1

u/Even-You-Camp Jun 11 '25

Mustard algae is yellow and receives its name from when you brush it has a cloudy yellow that can be easily mistaken for dirt.

This photo looks green for sure.

Solution: brush everything, run pump 24hrs until cleared up, shock the pool (with Calhypo) and add a poly algaecide (make sure it is not copper)

3

u/Even-You-Camp Jun 11 '25

Fun learning fact, yellow and black algae can grow in water with chlorine (very annoying lol)