Tank Specs: 75gal DT (9 fish, 14 frags) 40gal sump with fuge. (Actual operating volume roughly 30gal) Sal-1.025 Temp-79 Ammonia-0 Nitrite-0 Nitrate-5 Alk-9.2 Cal-435 Mag-1480 Lights -RapidLED kit. Intensity settings RB-70%, white-50%, UV-50% Carbon - yes GFO - yes Almost a month ago I notice diatoms on the sand bed. I changed my RO/DI filters and resin, which had not been changed since I started the tank a year ago. I'm assuming my RO/DI water was the source of the silicates that caused the diatom bloom. But it has been roughly a month since I changed the filters and the diatoms are still here. I've done several water changes and I've vacuumed the sand bed, but it hasn't helped. It's not on the rocks, just the sand. I'm not feeding any more or less than I usually do, which is typically twice per day. Does it usually take several weeks for diatoms to go away? I can't think of anything in the tank that can be fueling them. Any advice would be greatly appreciated.