I found that Iron and potassium are missing from the nitrate nitrite mixture from the fish waste.

I was told to just place a net bag of rusty nails and tin cans in the flush tank and that would get iron salts to the plants.

but what about potassium? does anyone have an idea on how to make a natural potassium that wont kill the fish?

we don't have the luxury of a nursery where we can buy plant supplements and even if we did most will kill the fish.

Any suggestions?

Thanks