You can already see from your original pump that the pump heads them self are letting the air into the line that feeds to your tank. I just bought mine 2 weeks ago and set it up. Had it set up to dose 25 ml which is 10 more then the BRS pumps were going to get my levels back up to par. Levels were still dropping! just upped it to 35ml yesterday. Now looking at the pump tubes in the day light, you can see there is a huge air bubble going from the pump heads in to line that goes to the sump. Very disappointed about this. Air bubbles in the tube mess up the dosage mls and can never keep it accurate. will be returning mine if i can.