One last thing ... intake reaching to bottom of tank
Very informative Paul always wanted to try the C series but never saw them locally until recently. My lfs now has one, think I may pick it up for an upcoming project.
I purchased my Fluval C's in 2013 & 2014. At the time, I had to go with two C3's on my 38 gallon tank because I was short on space between the wall and the tank. The one problem with the C3 at the time was that the filter intake was not deep enough to pick up waste from the bottom of the tank so I had to purchase the extension .... which at the time was $7, making it cost almost as much as a C4 which does reach to the bottom of a standard 29 or 38 gallon tank.
Right now on Amazon, the C4 runs $55 and the C3 runs $45.
https://www.amazon.com/Fluval-14003...UTF8&qid=1495622058&sr=8-1&keywords=fluval+c4
However, for that little piece of plastic extension you need on the C3 to reach the bottom of the tank, they want $14, making it cheaper to buy a C4. I run the C4 on my 29 gallon at "minimum flow" .... whereas when I had a C3 on it, it ran at "maximum flow."
Pre-Filters
I use pre filters and rinse them out weekly. On the C3's, I use the generic pre-filters and only have to change out the pads about every six weeks. On the C4 which has a larger diameter intake, I use a filter-max pre-filter and only have to change out the pads every two months or so.
Chemical Chamber
I think everyone pretty much knows that carbon is useless, but some people just put more bio-media in the chemical chamber. Putting huge amounts of bio-media in does nothing. Once you "max out" your bio-meida, the beneficial bacteria count stays the same (only as much as your fish waste can feed it) and it's just spread out over a larger surface area. Accordingly, I add a bio-bag of Seachem Matrix plus 100 ml bag of Seachem Purigen to the chemical chamber which helps keep the water crystal clear and lasts about six months. It's re-chargeable in bleach ..... but I just throw it away.