power heads basically just gives a tank a bit more circulations so u dont get any dead spots.
about couple of weeks ago the cheap Nova pump craped out so i've replaced it with a 1000L/H pump, the tank is about 60L so it turns the water just under 17 times every hour which is not quit enough.
a canister does not create much of a current at all as its not what its designed for but is great as an extra filter system along with a power head.