Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Plants need over a dozen elements to survive.
Water supplies H and O.
CO2 can be a problem. No matter how many fish you have that is not enough CO2 for a high tech tank. A low tech tank gets CO2 from decomposing matter in the substrate.
Water changes with water that has a GH over 3 German degrees of hardness provides Ca, Mg and some traces.
Fish food can supply the needs of the plants to a certain extent. It is reasonably rich in most of the other elements (N, P, most traces). It is low in K, Fe. Feeding more food overloads the tank with N and P before you reach a good level of K or Fe.
You need to prepare the substrate in a way that will provide the missing elements. If you use a quality substrate (not sand or gravel- high CEC material) and add slow release sources of potassium (Greensand) and iron (laterite) then the tank will be self sustaining for the longest time as long as you run it as a low tech tank. You do not have to overstock it to do this.
These sources are all slow release, though. Great that there is a steady, low trickle of nutrients into the system. Keeps it stable.
But all of this put together is not enough to make a high tech tank.
Simply adding more fish is not the answer.
If you had a table, and wanted it taller, you could not simply lengthen one leg and make it a taller table.
Similarly in an aquarium, to make a low tech tank into a high tech tank you need to work on each part of it in proportion to the others:
Macros: N, P, K.
Secondary nutrients: Ca, Mg, Fe.
Micros: all the others.
You can get sort of a half-way in between tank by adding substrate ferts. Tablets that you just have to add once every few months can supply a lot of the nutrients in a somewhat easier way than daily dosing, and can balance the fish food if you select the right ones (higher in K and Fe, moderate in other elements).
Carbon in some form is needed. Excel, DIY/yeast-sugar, or pressurized are your choices.
If your water is too soft (GH under 3 degrees), or else you find it drops through the week as the plants and fish use the minerals, then you can add GH booster, or something like coral sand in a bag in the filter. GH booster would be once a week when you do a water change.