Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Plants need about a dozen elements to grow.
Water and fish food add most of them, as long as you want only the easy plants that grow slowly.
For faster growth and a wider selection of plants you need to add the elements that are in short supply.
Hydrogen and Oxygen- if your tanks are lacking this there is a much bigger problem!
Carbon- You can use a liquid supplement, but you are right, Vals are not thrilled with it. Low dose seems OK.
Nitrogen, Phosphorus, Potassium: Plants use more of these than the rest of the list that follows. Fish food offers a fair amount of N and P, so if the NO3 test stays in the pink (at least 5 ppm) then do not dose N or P. If the NO3 test keeps dropping to zero then dose both N and P. Fish food does not have enough K. So dose potassium (such as Leaf Zone).
Calcium, Magnesium are used in moderate amounts, and most tap water has these minerals. If the GH is over about 3 German degrees of hardness, then I would not worry about these. If you suspect a deficiency you might need to test more to see what the actual levels of Ca and Mg are. If the GH is under 3 degrees, then I use Seachem Equilibrium.
Iron is the other mineral that is not supplied very well by fish food. Leaf Zone is good.
All the other minerals are lumped together as Trace Minerals or Micros. Seachem Comprehensive is one possible source.
If you want to start with dry materials (the actual active ingredients in most liquid fertilizers) then look into the Estimative Index.
Fertilizer tablets that you put under the sand can be a good way to get many minerals to the plants. Read the label to see if they have what your tank needs. Push them all the way to the bottom so they do not work their way into the water column.