aqua_chem
Aquarium Advice Addict
In a self sustaining tank? You can't really, that's part of the problem. These nutrients get sequestered away in plants, effectively 'leaving' the system, so you will always eventually run out. It's no different than a planted aquarium in that you need to constantly dose fertilizers. The only think that I can think of is some sort of sustained release system that would last for long periods of time, but I don't know how would be able to supply all the minerals you need, eg iron. Maybe a higher end planted tank substrate?
For magnesium specifically.... maybe dolomite? Would also add base, but also calcium.
For magnesium specifically.... maybe dolomite? Would also add base, but also calcium.