09-01-2012, 09:14 AM
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Although you can use a sump for larger tanks, canister filters are the norm for even very large (larger than 90g) Freshwater tanks. I think a good canister filter is much easier to maintain than a sump tank down below.
If you do go with a sump, there is no secret and filtration media is no different than any other filter with respect to mechanical, chemical and biological media. One exception might be a drip system using bio-balls or the like. The first layer is mechanical - filter pads, polyester filter floss or the like to remove large waste particles. then usually through a drip tray onto bio balls or the like. Actually I've heard that nylon pot scrubbers (check your local dollar store) works every bit as well as expensive bio-balls and the like. You might also consider products like bio-max or Matrix. Often the sump can take advantage of deep sand and with lights become a well planted refugium as plants have an amazing ability to use all sorts of 'nutrients' from the water resulting in a much cleaner water. There are also many. many synthetic resin products that might be used in a sump to adsorb impurities as required (Activated carbon, Purigen, Nitrate/phosphate removers to name just a few).
So there is no precise recipe beyond the basics and you would no doubt experiment to achieve a desired water quality for your tank.
Still....and for what it's worth, if I was setting up a 90g (or even a 120 or 220) freshwater tank, I would most likely opt for a canister filter rather than a sump.