Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
There are charts with the Estimative Index method.
One chart might say for tanks from 20-40 gallons, for example. If you have high light, CO2 you might use this for a 20 gallon tank. Low light, Excel or no carbon, use this much for a 40 gallon tank.
Try it, see how things go, then modify as needed.
I started off like that, then found that:
a) Big fish load added so much NO3 to most tanks that I did not need to dose so much.
b) Fish food also seemed to supply enough Ca and Mg, so I did not need to add Equilibrium, Epsom salt or other.
c) Potassium was still too low, so I added K2SO4.