Media for Sump Filters
Alfagrog is an extremely porous biological media with an excellent surface area for bacteria to live on. You can purchase this media in large sacks that will be more than enough for a large aquarium. Rather than tipping all the alfagrog into a chamber in your sump filter, you might be better off using some kind of media sack. With all the will in the world you are not going to stop 100% of debris from reaching your biological media. It will need to be cleaned occasionally and it's a lot easier and quicker to lift out a sack full of media, rather than having to remove the media manually hand by hand.
Bac bio balls are by far my favourite sump filter biological media. These can be purchased in sacks of 1000 which is enough biological media for any size tank you will ever have in your home. Resembling small pronged balls, they have a great surface area for bacteria to thrive on. The other advantage is they do not collect debris and dirt. That doesn't mean that the chamber they are in will not collect debris, you will still need to clean out the chamber occasionally. I would also recommend using some kind of media sack to contain all the balls, it just makes your life easier when cleaning the sump filter.
Flocor filter media is another great biological media which has a fantastic surface area like bac bio balls. I would use them in exactly the same way as bac bio balls.
Scrubbies - these are actually dish scrubbers, yes really, what you use to do the washing up. However, people have found that they make excellent biological media. You can probably buy a whole packet for a dollar, a lot cheaper than other biological media, but will perform the same function.
Filter media brushes- please make fantastic mechanical filtration and are best placed where the water enters your filter. The brushes will catch the larger bits of debris like uneaten food. Don't be afraid to put in several brushes, especially if you have a lot of fish. These media brushes are very easy to clean, you simply rince them in aquarium water.
Filter media foam - this foam is much less coarse than Japanese matting filter media and therefore is excellent at catching the very small pieces of debris that may find its way through the Japanese matting. I think it's very important to remember that you must clean these foam filters fairly regularly as they will become clogged. They are very easy to clean, just rinse them out and a bucket of existing tank water.
This is very coarse media that makes excellent mechanical filtration. I found this to be one of the best types of mechanical filtration to use in a sump filter. Don't be afraid to put several layers in one chamber which will collect nearly all debris. This type of coarse media will also act as biological filtration as well so you have the best of both worlds. It's easy to clean in a bucket of existing tank water and will last for years.
K1 Filter Media - this media claims to remove nitrates as well as ammonia and nitrite. This media will also require minimal cleaning and therefore would make great media for your sump filter, although it is rather pricey.
All the above biological media can be enhanced and made to be more efficient when used with extra aeration, or used in a trickle filter. It's very easy to incorporate a trickle filter into your sump filter. You don't have to you have the whole filter working as a trickle filter design the filter so just one chamber acts as a trickle filter and you will have a superb filtration system.