Does anyone know what is causing this to show up in my tank? Its like a brownish gold showing up on the sand and the returns and on the sand its kind of thick mat. I do use rodi water with a reading of 0 tds the tank is 3 years old phosphates have always been about .33ppm and I have gotten them down to .11 in the last few weeks. Any clues? I haven't added anything new to the tank or changed anything.
Thanks
Thanks
