If you have it you will know. Its almost florescent yellow to green and its much harder to eliminate. You need to raise chlorine levels quickly and keep brushing and vacuuming and cleaning the filter (mine is DE - not sure about other types). Clean all Pool toys with chlorine water from a highly shocked pool and wash swin suits. This stuff live out of water for a long while and it will come back if you give it a chance to.Is mustard algae really that common? Seems like it’s coming up a lot, myself included. I wish there was a way to positively ID the type.
Mine came back and I was totally defeated. Took a deep breath and NUKED the pool with Liquid shock. All toys in pool along with swim suits. 2X daily brushing and daily filter breakdown and cleaning. It was not fun and getting rid of it was very disruptive to my daily life. I am on top of my chemistry bc I don't want to deal with that ever again !