To provide some oxygen for the fish. I have a 29 gallon aquarium, and the air pump is for 20-60 gallon aquariums. I got a 14 inch air stone with it, and after turning it on, I found that it was a lot more power than I expected. It creates a rather strong current, one that I think might be rather strong for my fish. They have a rather hard time moving against it. Is this really a problem? I would imagine it can't be good, should I get a smaller air stone or something to that effect?