Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Plants will also remove ammonia, but that is too many fish. Too much ammonia. And, as has happened here, the plants cannot take care of it all.
The bacteria that remove ammonia turn it into nitrite. They grow pretty well but they do need some ammonia. Obviously enough were alive in this tank to turn a lot of the ammonia into nitrite.
The bacteria that remove nitrite, and turn it into nitrate are very slow growing. In this tank there may be a few, but nowhere near enough to remove all the nitrite being produced by the first group of bacteria.
If you were starting an empty tank (no plants, no fish, but all equipment running, substrate and decor in place) and doing a fishless cycle using ammonia from a bottle it would take about 3 weeks to grow a big enough population of both sorts of bacteria to support a reasonable fish load.
To make the bacteria grow faster start with some bacteria. Most plants will have some of these bacteria on their leaves and stems, so you did introduce some of these bacteria this way.
The population of nitrifying bacteria will be proportional to the amount of their food (ammonia and nitrite) in the tank. There are a few plant leaves dying and releasing ammonia, but not very much, so the population of these bacteria is very small.
What I would do now:
Keep up the water changes to keep the ammonia under .25 ppm and the nitrite under 1 ppm. Keep a dash of salt in the tank until the cycle has finished and the nitrite consistently reads 0 ppm.
If you can find some Tetra Safe Start or Dr. Tim's One and Only these are the actual species of bacteria you are trying to grow in this tank. All other 'bacteria in a bottle' products do not have the proper species of bacteria, so do not waste your money on them.
A larger tank would be better for that many fish.