Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I would set up a test, perhaps in a jar or small plastic storage bin (like a shoebox size)
Try whatever blend you want, and see what happens to the water column over time.
It may be that whatever ammonia is in the various materials will be locked up or converted by the bacteria to nitrate.
I would set up the test like this:
Set up 3 tests for each fertilizer:
1) Pure sand and water with each of the fertilizers you are proposing to use in a separate container.
2) Aquarium substrate with microorganisms and the fertilizer.
3) Aquarium substrate with microorganisms, plants and fertilizer and feed the 'tanks' with fish food.
Use the substrate that you are using in the aquariums. Actually take some of it from the tanks, since it will have all the microorganisms that are growing in the tank. If you cannot spare very much from the aquariums then use what you can by scattering it on top of some other material. Best would be if you had some left over substrate from when you set up the tank. The microorganisms you get from the tank will colonize that.
Fill with water, dechlor and whatever other things you are using in the aquariums.
Set up a bubbler or something so there is some water movement in all tests.
Add a plant or two. It could be planted in the substrate or drifting in the water. Or both. I would be pretty generous in adding plant material. But make all the planted tests start with the same amount and species of plants.
Feed some virtual fish, just as if there were real ones in there. The fish food you are adding to the real aquariums is supplying some nutrients, so you are trying to replicate the real aquariums without risking the fish.
Monitor several things:
All the aquarium tests you have, but especially ammonia, nitrite and nitrate. GH, KH, TDS will also help. If you have other tests like Fe, Ca or others, do them, too.
Plant growth. Especially note odd growth that might mean a deficiency or a toxicity.
This is why you started several tests. Your test 'tanks' that you are feeding fish food might go through a nitrogen cycle, and the fertilizer might contain ammonia. While you tried to bring some bacteria in from the established tanks, it might not have been very much.
The fish food will supply ammonia as the protein breaks down. If these 'tanks' show ammonia spikes, followed by nitrite spikes, then the nitrate starts rising then that may be from a combination of fish food and fertilizer, or just fish food.
If the tests that are fertilizer only, no fish food, go through a similar cycle then you know the fertilizer is adding ammonia to the water.
Once that cycle is complete (takes up to 3 weeks if you added no started colony from the cycled aquariums' substrate) you will continue to monitor the conditions.
Here are the results I would look for:
1) Does the fertilizer add ammonia? If yes...
2) Does an established bacteria colony have enough population to turn that ammonia into nitrate fast enough that the ammonia (and possible nitrite) is not a problem for the fish?
3) Does the fertilizer add anything else in amounts that are toxic to the fish?
The aquarium tests may help with this (Fe, TDS, other) but you might have to actually add some fish to see. Make sure the fish are acclimated to the TDS of the test 'tanks' so that if they do get sick you know it is not because of osmotic problems.