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It looks like you have the air hose hooked up to it which will draw air if you have it outside of the tank. The purpose for this can be many different things from just liking the way it looks with all the bubbles to using it as a kind of surface agitation. If you don't like it the pump will be fine without the airline hooked up. I believe I have the same powerhead running my skimmer but I can't really tell from your pictures. Petco brand and costs anywhere from $15-$30 and I've been running mine for 2 years now without the airline.
I thought there was wasn't sure as the pict is so dark, beej hit it remove air line
I never run this type of power head with out under gravel filter towers but I know they can be ,