>> Anyway I've decided I'm sick of wasting money on rubbish diaphragm air
>> pumps so got a power head and filter all-in-one thing (Fluval 1). It
>> seems to be going great, and my fish seems to enjoy the current (and
you
>> cant beat how quiet it is!). Anyhow my question is what about air?
Air bubbles don't add oxygen. It's the water circulation that oxygenates.
It cycles CO2 laden water to the surface, where CO2 can escape and oxygen
can reenter. Any pump or filter system that circulates water past the tank
surface will oxygenate the tank. That includes powerheads (whether or not
air mix is turned on), and your internal canister filter. It sounds like
your tank should be fine.