We have a 40 gallon tank and I did a one week conditioning and ran the filter. I did this based on what petco told me. I then got 3 glofish and found that they need to be in a group of 5 or more. We went and got 3 more(we have 1 of every color cept 2 purple), 4 glass catfish for the medium feeders, and 2 dojo loach for bottom feeders. Currently they seem fine but it has only been a day. I do have one glass catfish who seems in love with the heater. I find that weird since there is a boat and skull to hide in and some plants but he prefers the heater. As I have learned on this sight I keep the light on for 8 hours. Have a bubbler. This weekend I will be attempting a partial water change so that should be fun.