"This is my first try with a cannister filter and when I first bought it, I was very disappointed. I was about to try to return it! The maintenance and assembly were HUGE pains! I also noticed that it didn't circulate the water quite right and my fish were gasping at the top of the tank for oxygen - a pretty frightening sight in a tank full of adult discus!
However, as time went on, I noticed a few things. Each time I cleaned the filter, the aeration was better. Also, when I experimented with the position of the exhaust, I was able to overcome the aeration problem and found that by moving it in the right direction I could get proper surface agitation without even adding a powerhead.
Next, this filter replaced an outside biological filter that had broken down. There was alot of debris in my tank and at first I had to clean it weekly since as soon as enough debris built up in the filter, it's aeration ability REALLY suffered. But after a month of operation, and dealing with the downsides, it was operating flawlessly and now I only have to do the recommended upkeep. My water quality is excellent and 2 pairs of my 8 discus are spawning regularly. My water is spotless and my fish seem really happy. If you're willing to experiment and play around with it, it is a great product. Just be gentle when cleaning it or you could end up with a real mess."