Think I have mustard algae

[chem geek]

Most important for getting rid of yellow/mustard algae is to completely eradicate it. That means getting behind light niches and under removable ladders and other shady areas, especially with poor circulation, where the algae likes to hide out and grow. This algae doesn't like direct sunlight. It requires roughly double the active chlorine level to kill it compared to green algae. You also need to disinfect your pool tools like poles and nets so can put those in the pool at least part of time that you have an elevated chlorine level. Worst case, you can use a phosphate remover, but if you eradicate it then you won't need to worry about phosphates and having to buy another product to maintain your pool other than chlorine.

[BigDave]

Our pool has had recurrent mustard algae for the last couple years and I have been unable to eradicate it with very high FC levels for extended periods of time and daily brushing. I suspect that it has found refuge in our solar heating panels. This summer I'll try reducing the phosphate level.