Some cheap little one that came with the tank. To tell you the truth I don't think I'm going to put it back in. The hood of his tank has a hole for "feeding", and he gets plenty of air. The day right after I took the pump out I took the hood off to feed him and he was swimming around the top flaring his fins like he was trying to say "Hey papa look at my first bubble nest".
Ahh okay :) I find I always have trouble with those preset pumps. Loud, or don't work. There's this one filter I have made for the "goldfish starter kit" 1.7 gallons... On low in a 10 it shoves my stronges swimmers around. :/