Thanks, I've been looking for a tank to upgrade to. (AKA raiding the consignment shops to see if they have tanks. I saw a 30 gal) I think I've regained control of the cycle as the goldfish hasn't had any further problems after I made sure to change some the water daily and switched the filter cartridges from a cycled tank. As soon as I can find another larger tank I'll upgrade.
petco $1/gallon sale is coming up in a few weeks.if you can swing it i recommend a 40 gallon breeder tank.then your fish can get a friend.