I’ve had “mustard algae” for a year and a half and have literally tried everything in the books to kill it and most things twice. We even changed the sand in our filter to zeolite and the laterals looked fine to us plus the seals and all. I get splotches of sand colored stuff in the bottom of my pool. We vacuum to waste constantly plus have tried everything. I’m almost to the point of honestly thinking it’s sand. When I touch it, it doesn’t feel like sand nor is it slimy. It goes mostly to wherever isn’t getting the most circulation. It turns white when we shock it or use yellow out, black algae killer, algaecide, or whatever it may be that we are using at the time to kill it. I want to put a cloth on my jet to see if anything comes out, but the jet is very powerful and I wouldn’t know how to put something like that on there and it stay. The “algae” does go away easy but, it returns not necessarily in all the same places but, it does get into cracks and other places in my pool. I will attach some photos but, the color isn’t it’s true color in the photos. I am at a loss and I hate not being able to use my pool. It’s only 3 years old. The black specks are big debris and the last photo is it when it’s white. It’s hard to see. Please help, it’s driving me crazy. The pool store doesn’t believe it’s mustard algae and I just had phosphates for the first time just in the last 2 weeks and they are over 2k. We have stuff to get rid of them.