My fish arnt in heated tanks, nor is it filtered, i just change there water. Iv never really been told how much to change them, but i do once a week. There isnt ani thing but those rocks in there. I do have bigger bowls i can put them in, and have lots of fake greenery that can b placed inside for them. Later in march, i am getting a five gallon tank, that will b heated and filtered, its just the point where im trying to keep them healthy long enough to live till i get it.