Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Fertilizers for garden plants, row crops and other land based growing methods are different from fertilizers for aquarium plants. The biggest difference is this:
Land fertilizers are applied to the soil. The soil is relatively dry most of the time. There is high oxygen and moderate to low water compared to an aquarium.
Fertilizer applied to the soil breaks down in those conditions at a particular rate, depending on what the fertilizer is made of, but the key is that it breaks down, and interacts with the soil, water and air that is in the soil in a certain way.
When you put that fertilizer under water it may react differently. There is less oxygen in an aquarium substrate, and a lot more water.
That may make a difference, not so much to the plants, but to the fish, shrimp and snails in the aquarium.
When some of these fertilizers are used on the land they can kill or reduce the micro- and macro-organisms in the soil. Bacteria, fungi, earthworms, insects and many other things sometimes do not live when certain fertilizers are used.
The same problem happens with fish etc.
If you have access to some of that fertilizer I would test it separately from the aquarium, and not just use it right away in the tank.
1) Put a few grains in a jar of water and test with all the aquarium tests you have, but especially ammonia, nitite and nitrate. GH, KH and pH, too.
2) Put a few grains in a jar and cover it with some of the substrate you are using in the tank. Same tests.
If all the tests show that the fertilizer seems to be safe for fish, then set up a separate container that is similar to your tank. A few grains or more of fertilizer, covered with the substrate. A cycled filter, or share some media from the cycled filter on an established tank. Plants. Then add a few fish. Run the same tests, and also monitor the fish.