Ok. Then it's probably the 750gph model. I don't think I'd feel confident with a single 750 gph
power head in a 4' tank. When you buy your second one, get a 1200 or 1400 gph
unit. I think between the two of them you should have pretty good flow.
Take those suggested tank size recommendations with a grain of salt.
I would probably keep the air stone until then.