Are you sure nothing could have tipped into the tank? Someone on my tropical forums had this happen, but his cat knocked something into his tank lol
If you take everything out and clean the tank, it's pretty much a new tank again. When your tank is cycled (something that size will cycle) good bacteria grows on everything (filter,rocks,decorations,walls) and when you take it all out and clean it, you get rid of all the good bacteria that kills ammonia and such. If your tank is recycling, I would test the Ammonia, NitrItes and NitrAtes :( Do you have somewhere else for your boys in case your ammonia gets too high?