Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Fish food supplies fair amounts of N, P, and trace minerals.
It is fairly low in K, Ca and Fe.
Tap water might supply many traces, Ca, Mg, and N in the form of ammonia (from chloramine).
A low tech tank (low light, no CO2) might have enough of most fertilizers from fish food and water changes. If not, then I would first dose K and Fe.
You are adding carbon, so the next step is to use the EI method, but monitor all the things you have tests for. I would start with half the basic recipe for a low tech tank.
Macros: N, P, K.
Sources include fish food, water changes and KNO3.
Test NO3 and keep it between 5-20 ppm.
If the level keeps going too high while you are dosing ferts, then use less.
Sources include fish food and KH2PO4.
I do not test for P. I go by the Nitrogen. If I do not need to dose N, then I know the fish food is supplying enough N, so I assume it is also supplying enough P. If I need to dose N, then I dose P in the same ratio as the EI recipe.
Sources might include some water, but not always. Fish food is pretty low. K2SO4.
I have heard it is pretty hard to overdose K, and when I skip dosing the plants show deficiency. Small holes that start brown, then black, then leaf tissue falls out. For me, this was mostly on Java Fern.
Secondary nutrients: Ca, Mg and a few others.
Generally supplied by fish food, tap water. GH booster, such as Seachem Equilibrium.
If the GH of your water is at least 3 degrees, then assume the Ca and Mg are OK. If you see deficiency signs of one or the other it might be worth testing for each mineral separately. If you are keeping hard water fish (many live bearers, certain Cichlids, certain Rainbowfish, others) then use GH booster to get the water into their preferred GH. Read the label, and do not buy a GH booster that include sodium chloride (salt).
Traces or Micros include about a dozen minerals that the plants need in very small amounts. The only one I will discuss separately is iron.
Sources include fish food, tap water, fertilizers. Fish food is not a good source of iron.
CSM+B is one common trace mineral supplement. Some people add extra iron at the rate of 4 parts CSM+B to 1 part chelated iron.
Chelation is a method of combining the mineral (in this case, iron) in a way that most chemical processes in the aquarium (or garden soil) will leave it alone, but it can be broken down to make the iron available to plants.
Here is how I would do it:
1) Read the EI recipe.
2) Figure out how much of each material you might want to add to the tank for 2 weeks.
3) Mix one bottle with macros and a separate bottle with micros. If you need GH booster just use it once, when you do a water change.
4) Dose at half the normal rate for a low tech tank.
5) Monitor the NO3, GH and any other tests you have. If there seems to be a problem then adjust what you are adding.
6) At the end of 2 weeks see if the plants are growing better.
7) Make adjustments to the recipe and do another 2 week run. You ought to fine tune the system pretty fast. Keep the test equipment handy so if you see a problem you will have one more tool to help figure out what is going on.