Checked everything and I know it's the closed loop. I am not using any spnge on the intake for the mag7. I am running two 90's to get up and over tank, then one more leading to pump, all 1 inch pvc. Then a reducer to go to the mag7 which is 1/2 inch. Then coming out I go back to 1 inch from the 1/2. I have checked all the glued sections and covered in silicone, so I don't think there is any air being sucked in. I have read alot about cavitation and was wondering if there was a way to check to see if that is whats causing the problem. I have checked all the glued sections and covered in silicone, so I don't think there is any air being sucked in.