It is more than possible to have a sterile tank. I have never been an advocate of immaculate tanks just clean ones
The diatom filter may be removing the food sources if run too often and reducing beneficial bacteria. They should not be used continuously. Once a week at most to polish the water would be better (or even 2x monthly).
In this case I do not think that will be the issue. Bacteria does have an effect on the overall health which reduces the organics in the tank but will not really be the direct cause. If this is cyano
, your main concern will be PO4
. Often introduced through unpurified water or foods.