Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
The plants do not sound like they are very much, but they are helping some.
The tank they came from, with fish, would have supported a certain amount of nitrifying bacteria growing on the surface of the plants, on leaves, stems and roots.
So, it seems to me that you brought in enough nitrifying bacteria to jump start the cycle, and the plants are helping out.
I would continue to monitor things, and not add more fish until the conditions have been stable for a week or two.
When you are ready to add more fish you might add some Nitrospira species of bacteria to the tank. These are the correct species of nitrifying bacteria.
The grow to match the waste load in the tank. When there are few fish there are few bacteria. When you add fish there is more waste than the bacteria can handle.
By boosting the population of bacteria the fish are protected.