what the purpose of a powerhead?..i have one and the fish didnt like going on that side of the tank so i turned it off, well the next day i turned it back on and now they swim in the current that the powerhead makes, kinda like they are swimming upstream i guess.

here's another question..i have 1 albino rainbow shark can i put a bala shark in the tank also...fyi its a 55 gallon tank...saving up for a 175 or a 190 gallon...will need one when my babies grow-up..i have danios (giant and zebra) gouramis,loachs, cherry barbs and ottos

powerheads provide circulation in the tank, which help increase oxygen distribution. and as you noted, provide fish stimulation and exercise.

Powerheads are often used to generate suction in the riser tubes of undergravel filters, and they usually have a venturi (air entrainment) combined which can be both more fun for the fish and provide airation. If you don't have an undergravel filter I would stick a cilindrical foam sponge over the intake(avaliable for this purpose in aquarium stores) for particulate as well as biological filtration. I would always airate a tank with a powerhead venturi over a bubbler and air pump, because powerheads are silent, and I've yet to find an air pump that is. If the current is too strong you can usually attatch a deflector to the outflow, and there are other ways of reducing current as well. P