snail die off does not cause brown diatoms. What kind of lighting? 12 hours is a lot... And if it isn't calibrated there is no way to "figure"...
But, if you are getting GSA, I would dose Macros 4-5 times per week, at 2 pumps a day. Do this for a week or two and reassess.
But, if you are getting GSA, I would dose Macros 4-5 times per week, at 2 pumps a day. Do this for a week or two and reassess.