Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
1) What is the GH of the tap water (or whatever you use to fill the tank)?
2) Is this the right value for the fish?
3) Do you think the Ca: Mg ratio in the tap water is about 4 parts Ca: 1 part Mg?
1) If the GH is at least 3 German degrees of hardness then the Ca and Mg is probably OK for most plants, and soft water fish.
2) If you are keeping hard water fish, they prefer a GH over 9 German degrees of hardness. Research the fish to be sure.
3) You could look at the water quality report from the water company, this may tell you. Or, there is a way to calculate it if you have a calcium test. The ratio does not have to be exactly 4:1. If you suspect the magnesium is too low, then dose MgSO4. If you suspect the Ca is too low, then dose calcium perhaps calcium chloride. If both are low, then use a complete GH booster, such as Seachem Equilibrium. This has the right balance of Ca and Mg, plus some potassium.
1) Does the NO3 from fish food stay high or climb between water changes?
Fish food contains reasonable amounts of N, P and most traces. Low in K, Fe, Ca, Mg.
If the answer to this question is yes, (the NO3 from fish food climbs between water changes), then the plants are not using it all, and they are also not using all the P or the traces from fish food. No need to dose the full EI amounts of KNO3 or KH2PO4.
But fish food is low in potassium. Dose K2SO4 to give the plants potassium.
Lets say you decide to dose only 50% of the KNO3 in the EI recipe, because you know the fish food is supplying the other 50% of the nitrogen, based on the NO3 test.
Then you can assume that the fish food is also supplying about 50% of the phosphate, so dose 50% of the EI recipe for KH2PO4.
But this leaves the plants low in potassium. In the full EI recipe KNO3 gives the plants both N and K. So you need another source of K. This is K2SO4.
Whatever amount you have cut out of the KNO3 dose, make up for it with K2SO4. If the EI recipe says 1/2 tsp KNO3, but you only dose 1/4 tsp, then add 1/4 tsp K2SO4.
Also, only dose 50% of the trace minerals, but add a little more iron.