HI, about the fish hanging out on the top of the water---maybe I can tell you of an experience I recently had. I had a 150 gal tank with a RES and 18 assorted goldfish along with a bunch of HOB filters. I got a great deal on 3 Cascade 1500 canister filters so I replaced the HOBs with the canisters. The next day all of my fish were at the top of the tank, rarely venturing into the lower depths. I did a couple of water changes with minimal effect. I went to Petsmark and met a lady who appeared very knowledgable about fish so I posed my problem to her. She seemed to know immediately what the problem was. She asked if my old filters had a waterfall effect which constantly broke the water (it did) and if the new filters also had this water-breaking effect.(it didn't) She said that the waterfall effect caused more water to come to the surface to pick up oxygen and that new filters did not provide this. Hence there wasn't enough oxygen in the water for the fish. She said to get an air stone or bubbler which would cause bubbles to rise to the top, breaking the water allowing more water to come into contact with oxygen, and give the fish more oxygen in their environment to breathe. I bought a cheap bubbler, set it up, and went to bed. Next morning everything was back to normal. Haven't had this problem since. Not sure if this is your problem but I thought I would mention it.