you know, a twenty would be even better and would cost 30bucks...if i ever get one i would use at least a 20 with a well working filter, when i fist had goldfish, i had only two years back and i had them in a ten, i changed the tank very often and the fish were fine, till one day they were gulping for air, i did not have a filter at the time, but now i wonder what was the cause of their gulping and eventual death? my theory is that there was not enough oxygen in the tank, perhaps a filter would of been the way to go since it could mix fresh o2 into the tank, however im still not sure what the real cause of death was? ammonia levels were low...any guesses?