I have a Eheim 2215. This specific one of my three with the issue, I got used from a petshop I use to work at about 1 year ago it was running there for years... Up until a few months it was working just fine. Now after running for a week or so (after being thoroughly cleaned) the water flow seems to be very weak. Pipes are not clogged, I cleaned them and cleaned impeller. What is going on? I have also removed media from filter thinking that maybe it was too packed , works initially but goes back to poor flow after a day or two. What can i do to remedy this issue? Love these filters. 