Diatom bloom

[gambs]

So I have been having this brown diatom bloom for a few months now and it has pretty much taken over all my rocks and equipment. I'm constantly cleaning the glass and the tank looks terrible. All my levels are at 0 , nitrates are at 80. There's about 20 or so Mbuna in a 90 gallon bow front. Ph is at 7.8. I have PFS that .5 in deep. Food doesn't ever settle but there is alot of fish waste that settles each week. I wc weekly about 40%. My question is how do I solve this diatom problem? Is the PFS leaching silicates? Should I change to aragonite sand? Any advice is welcomed as i am frustrated with this tank. I have a 125 with PFS about 3in deep with more fish with same water parameters an no algae or diatoms. Don't understand how one tank can have it and another doesn't when they are both the same.