Small tank(was only young), no filter. Just 100% water changes from the tap. They are hardy. Low o2 levels are fine with them. Heat maybe a prob in a classroom...
They live in swamps...they shouldnt need much water flow. Id clean mine out once it got dirty.
Places to hide are a main factor IMO
They get quite tame....i want one again....
How big where the ones he had and what food was used?