Could also try raising and lowering pump out of the water and slowly lower back in, sounds like you have air trapped..That that with my maxijet powerheads..had bubbles for ages untill i was told to do that...You get an initial blast of bubbles when it first goes back in the water, but then should clear..As a note though, i had to do a couple of times with a powerhead before it blew clear...I dont see why a powerhead and pump doing this should be different..Worth a try, nothing to loose...
Niko