I have a powerhead with a tube that comes out of the water. It has acap on the end that I can twist in order to control no aeration to wide open. It used to work perfectly. Now it doesnt matter if I take the cap off completely, no bubbles.
No bubbles means the venturi feature is not working. This could be because there is not enough flow through the powerhead or dirt being in the pipe. Especially if there is dirt or algae in the restricted section that is responsible for the venturi effect, that can stop air from being sucked in, and then there are no bubbles. I'd take the whole power head apart and give it a good cleaning :thumb:
I don't think my powerheads are too great, as I cannot tell who made them. They do have great flow however. That aside though, I notice the venturi effect doesn't work when I have the powerheads lower in the tank, I suppose they just aren't strong enough to pull the air all the way down the line to mid-tank or lower (6' 135g). I just have an air pump split between the two powerheads to make it happen for me.