Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Part of the problem is that in the soil it is not so totally wet all the time, so some fertilizers react a bit differently. Urea, for example works just fine in the garden, but not in an aquarium.
Anyway, I have heard of people using certain of the Jobes stakes products. (I am not sure which), breaking up a stick or two per 10 gallons and sticking it well under the substrate. Search here for more info about exactly which ones and the dose.
Osmocote is a garden product that works in aquariums. You need to get the pellets under the substrate. There are 2 ways that are commonly used: Freeze some in ice cubes and stick the ice cubes under the substrate or put the pellets into medicine capsules size 00 and stick these into the substrate.
Of course the simplest are the fertilizers used in agriculture:
KNO3 (also an ingredient in some stump removers, but not all)
Chelated Iron (at least 2 formulations, different chelating materials)
Other material from other industries:
Calcium carbonate (I have some labeled for spas) Raises the KH (and usually therefore the pH) and calcium level (thus the GH)
Muriatic Acid (Pool and masonry uses) for cleaning that REALLY bad stuck on mineral deposits. (Caution: If you are not accustomed to using this, do not.)
Epsom Salt (medical use) adds magnesium, raising the GH.
Table salt, Kosher salt: Medication for certain parasite problems in fresh water fish.
Baking soda: Raises the KH, and this can raise the pH.
Peat Moss (Pure Canadian Sphagnum) Adds organic acids to the water, and some peat moss acts like an ion exchange water softener. May lower the GH or KH, and usually lowers the pH. A substitute for 'Black Water Extract'