[Diana K]

Use the bubbler to run a box filter.

Nitrite is a natural part of cycling the tank.
Do enough water changes to keep the nitrite under 5 ppm, the bacteria you are growing slow down when the NO2 is over 5 ppm. They grow best with more oxygen, so definitely get more water movement going.

Pretty soon (perhaps a week or two) the ammonia and nitrite will both read 0 ppm. Then you can stock the tank, but that small a tank would be so easy to overstock! Just one fish, or a couple of small ones. Lock up the fish food, or else every child in the room will be feeding the fish, and you will have a disaster.