Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
The plants in the tank may be removing the ammonia at a rate that is enough to keep the Danios alive.
Anyway, here is the Fish-In cycle:
1) Test daily.
2) Do enough water changes to keep the ammonia < .25 ppm and the nitrite <1.0 ppm.
3) Add salt (sodium chloride) at the rate of 1 teaspoon per 20 gallons when there is nitrite showing. This is a low level, and is safe for the plants, but it is enough to protect the fish from Brown Blood Disease.
4) When the ammonia and nitrite have been zero for a few days, and the nitrate is rising the tank has grown enough bacteria to handle the waste from just the fish that are in there now. You can add more fish, but just a few, and go through the whole thing again, and again, and again...
OR THERE IS A BETTER WAY
1) Run, do not walk to the nearest store and buy a bottled bacteria product that includes Nitrospira species of bacteria. These are the very species you are trying to grow in your tank. Do not waste your money on anything else. Read the label. Do not listen to the sales help saying, 'But this other stuff does the same thing'. Order it on line if the local stores do not carry it.
2) Add a small amount (you only have a few fish) and monitor the conditions. If there was any ammonia or nitrite before you added this product it/they ought to be gone in 24-48 hours.
2) Now you can add more fish. Keep the bacterial additive in the fridge and keep adding it in proportion to the amount of fish you add. Add just a few fish, use just a little of the bacterial additive. Add more fish, use more of the additive. Be generous. You cannot overdose, except that it is wasted if you do not add enough fish to keep the bacteria fed.