Agreed, diatoms ... Your nitrates while not perfect are tolerable. Probably a consequence of your feeding pattern (which you are taking care of) and your water. Check and make sure the water is RO
water. If you are someone you know (lfs
?) has a TDS
, check the TDS
on the water. It should be zero or near zero. Otherwise it's probably mainly the overfeeding.
You did treat the tank with copper right? What was the product name?