I have been using a generic pyrex glass tank for about a month. For the last week I have been unable to prevent the carto from flooding. I've used 1,2, and three hole prepunched cartos. When I first started using the tank I was using the 3 hole and had no issues. I have kept my draw on the light side since this issue began. I don't have a filling tool. My suspicion is that the inner o rings are slightly damaged and are letting a small amount of air into the tank. I don't have a ton of experience with the carto tanks, so I'm kind of grasping at straws here. The tank is cobalt so its difficult to see what's going on in regards to bubbles. In retrospect clear would have been a better choice.