Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
My tanks have so many fish that the nitrate stays up there between 5-20 ppm, so I do not dose much at all. I also do not use GH boosters, except in my hard water tanks, so most tanks do not get any K that way, either.
1 teaspoon KNO3
1 teaspoon KH2PO4
6 teaspoons K2SO4
Mixed with enough water to dose all my tanks for a week. I am dosing something like 700 gallons worth of tanks. So, my 46 gallon is roughly 1/15 of the total, so it gets the equivalent of 1/15 teaspoon of KNO3 + 1/15 teaspoon of KH2PO4 and barely 1/2 teaspoon of K2SO4 every week. The fish food adds nitrogen and phosphate, so there really is not a deficiency, but there is also no buildup calling for weekly water changes.
I would look at the plants and use them as a guide: Any potassium deficiency? Dose more.
Look at the nitrate test: Does it get higher than 20 ppm? Dose less.