i think a pair of frogs would be fine, a person can overcome a messy pet w/ more frequent tank cleaning. i have had butterfly loaches in rather calm tanks before and not had any problems w/ them. i do understand that they come from faster moving current, but they seem to cope well w/ average tank life. the tank my local lfs keeps them in only has an undergravel and the butterfly loaches are active and healthy....but again i would recamend frequent cleaning....maybe twice a week. consider the fact that you are looking at putting 4 or 5 pets in a 5 gallon tank...their health needs to be considered