A power head is something some people hook up to under gravel filters in tanks... lots of guys on here just plug them in and hang them over the edge of the tank... They spray water and create a current to simulate a river effect. Some Piranhas enjoy swimming in it. Not adviced for piranhas under 3 inches though because they can get sucked up them. Don't want that!! Jake
That is if your powerhead is to powerful , mine are 1inchers, and they are fine it gives them oxgen in the tank as well. The reds like my fake coral that spits out airbubbles. I haven't seen them bubblesurf yet.
Yes, depending on the size of your p's and the size of your tank, they have differents brands and models. I think any size p would be fine as long as it's an appropriate size powerhead. It's not needed but is a great investment. Oh yeah some come with a prefilter, a sponge, so your little fishies wont get sucked up.