I would wait till somewhere in the 8-10 inch range before upping the tank size. It would also be best to step the gar up to the eventual tank size. For example move from the 30, to a 75 then the final tank.
Okay, so it's a standard 30 gallon. I wasn't sure if it was a 30 gallon breeder or not which is why I asked.
I would say that you should be fine until the gar hits 10" or so; it should be that length in no time at all. The main thing is to ensure that the gar can easily turn around.
Ok cool cool, I was wondering what kind of other fish I can put in. The thing is I have a blue lobster who has murdered 2 silver dollars and 2 barbs already, also have a standard crayfish so bottom dwellers wouldn't work. You guys have any suggestions?