These are the results I get using .12 (1/8) teaspoons in 1 ml water for
10 gallons of water (in a 12 gallon tank):

10.85 ppm Nitrate - target is 5ppm
6.85 ppm Potassium - (from KNO3)
8.54 ppm Potassium - (from K2S04)
15.38 ppm Potassium total - target is 20ppm

1.7 ppm Magnesium - target is 5-10

So yeah, I think that's a good starting point as your're getting near
enough potassium and magnesium without going overboard on the nitrate.
Remember though, your fish food adds an amount of nitrate so I'd only
do the 1/8 teaspoon dose along with a 50 percent water change weekly.
If -a you got lottsa plants, they might use all the nitrates which is
good, then you can start dosing more.

steve