Before you go taking the powerhead apart make sure your tester is accurate. I have 4 compression testers and all 4 are different. I took one gauge and hooked it up to my air hose with a regulator in between and set my regulator at 100 psi. I took the glass and the back off the gauge and bent the air bladder inside the gauge until it matched the air pressure on the regulator. Not sure if that’s wise but it worked for me. There probably is a more correct way to do it so someone else may chime in. But at any rate don’t disassemble it until your sure it really is low.
