Rainman, I do have an IBC tote that is my bio filter with bio balls and other plastic matter. This tank or "pond" what have you, is indoors. Stays right around 75-85 degrees inside all year.. I have radiant heat in the concrete and that alone heats the tanks in the winter, so that's nice. What kind if sand filter do you run? I also do about 1/4 water change on a daily basis which I believe has been keeping the ammonia and nitrite at bay. It's apparent to me that I need more oxygen to both my bio filter, along with the fish. Hetero and aerobic bacteria need oxygen just as much as my tilapi do.
