My tank finished cycling, it's been about 7-8 weeks. Here are my tank stats: PH 7.9 Ammonia 0 Nitrite 0 Nitrate 20 ppm I've been testing the tank every few days and the nitrates dont seem to be coming down. I had 0 nitrite at week 4. I'm also getting a lot of brown algae/diatoms growing all over my rock and tank walls. Here's my setup: 112G tank with 40G sump I'm using a vertex IN 180 protein skimmer, 700 GPH return pump and 2 modded maxi jet power heads pushing 1200GPH each. Plenty of flow IMO. For lighting I'm just using some 6500K compact florescents in some shop light cans (temporary setup). For substrate I'm using CaribSea Select grade reef sand. It's aragonite/oolitic. For rock, all I have is some DIY rock that I made out of oyster shell and portland cement. I cured it for 6 months in tap water. I use Instant ocean salt and a spectrapure RO/DI filter for my water. I have 0 fish, 0 Invertabrates but my nitrates are still high? What is the problem and how do I fix it? Thanks in advance, I can't figure this out.