Over the past month or so I am constantly getting diatoms on my sand bed. It is not cyano, it's golden brown powder and blows off easily. About 9 weeks ago I took all the fish out because of velvet. I did stir up all the sand (sandbed is only an inch or less). It is not going away. I don't know where the silicates are coming from or if I can even test for it? My filters in my RO/DI were changed a month ago. The unit is about a year and half old. The membrane has not been changed yet. That being said, I don't think its from that because my two QT tanks do not have it.