This filter is a great filter. I would suggest it for 10 to 20 gallon tanks, not the suggested 10-30 gallon tanks. This filter has better filtration than the ever so popular Bio-Wheel. People say that it is loud and that it doesn't fit with hoods on the tank, but that isn't true at all. I have found that with the intake tube extended all the way to the gravel that it keeps more mulm out of the gravel. When I did my normal gravel cleaning, there was less gunk in the gravel, and the water in the bucket that I took out of the tank was crystal clear. I love the adjustable outflow tubes that you can adjust for a wave like effect.
The living filter chamber never has to be adjusted, and the impeller hasn't been cleaned in over a year!! It is still pumping strong. I also like the lifetime warranty. If I have any problems, I just email Tetra and they take care of it ASAP. The only thing I don't like is that it doesn't work as well on lower water levels so if you leave your tank alone and let the water get 4" below the outflow of the filter, this power filter isn't for you. I give it 5 stars for crystal clear water and great water parameters!!
I also love the double cartridge system and the Regular Size Tetratec Pro II cartridges can be used in Whisper Power Filters models C, 1, 2, 3, 20, 30, 40, 60, and all Triad models.
The Tetratec Pro II Extra Large cartridges can be used in Whisper Power Filters models 4 and 5. They clog quickly if used in established aquariums, because the green side catches more stuff than other cartridges.