Are you using it with the venturi adapter? If so, that is why you are getting those bubbles...
If not, then your PH
must be sucking bubbles from somewhere else into its intake. Is there anything around it that is producing bubbles (i.e. sump return, bubble wand, etc...)
Or perhaps there is air stuck inside the impeller assembly. You might want to make sure you flip them upside down while under water (turned off of course) to make sure there is no trapped air anywhere inside the PH