I have a 65 gallon reef tank that has been running about 2 years. My MH bulb went out awhile back and it took about a week to get a new one in the mail. Since then I have been getting brown diatoms. They only show up in areas of the most light. When the lights come on in the morning there is no diatoms then they show up about 3 hours later until about late afternoon. After that the diatoms disappear twards evening. I don't understand why the longer the light is left on the diatoms disappear. And when they do appear it is in highly lit areas of the tank. Any ideas. I use RO/DI water and all tests are normal.
