While that's POSSIBLE... I'm not sure if it's very good for the fish.... While plants are more or less immune to an overdose of iron or magnesium, fish are much more sensative creatures.
The only thing i can think of that i can worked for me would be to drop a rusty nail in the water. Sadly, that only works for iron. I guess you could get a small lump of magnesium and throw that in as well but it might upset the pH.
Anyway, would you mind explaining your fertilisation reluctance?
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