i wouldn't use goldfish for cycling an aquarium because if your going with a tropical tank, your going to have to take them back later one, if they live. i wouldn't cycle with fish either, instead try fishless cycling (check for a stickie around here or someone else will tell you in this thread). or you can buy a 3oz packet of Bio-Spira to instantly cycle your tank and add fish the same day. (it works, i successfully cycle my 20G and many others have had the same results, use real live bacteria, not like products that don't work IE: Stress Zyme, Cycle, etc) only downside i see from this is that they are expensive. a 1oz packet cycles up to 30G aquariums, but cost $15 a packet. a 3oz cycles up to 90G and will probably be a bit more.