I agree with others, you don't need the canister filter so if it's broke I wouldn't bother with a new one.
Im my book there are seven types of filtration
- Basic Biological: This is Nitrifying Bacteria (NH4 -> NO2 -> NO3)
- Advanced Biological: This involves a more advanced method of denitrification (removes NO3) by adding a carbon source to the water and possibly a type of filter designed to create anaerobic conditions.
- Skimmer: Removes raw organics before converted to NO3
- Chemical: Stuff like carbon, GFO, ect (can aid in removing organic waste and phosphates)
- Mechanical: Stuff like foam, floss, filter socks, ect that remove particles from the water.
- Water changes: Removes NO3 and other contaminants while replenishing useful elements.
- Refugium: Growing and harvesting algae in a separate part of the aquarium (usually in a sump). Algae uses NO3 and phosphates to grow, thus by growing and harvesting you're naturally lowering these contaminants.
Everything except 1 & 6 is optional although some might argue with 6 but let's not get into that just yet. In saltwater live-rock is your 1 and it does it quite well even allowing possible denitrification which removes NO3 naturally. NO3 is nitrate which you want to limit to reduce algae growth and promote better coral and fish health. Skimmers aid in the reduction of NO3 by removing the organic waste prior to breaking down into NO3. Canister filters that contain bio-media are very good 1s, better than live-rock. However too good can be a bad thing as your skimmer will not function as well as it could because in a sense it doesn't have enough time to remove organics before they are already converted to NO3.
4 is typically only needed if you're really looking to polish the water and/or reduce phosphates for optical conditions for certain corals. They require some caution as they can shock the system if too much is used and there are risks involved regarding contamination that have happened in the past.
5 is a good idea however requires constant maintenance to prevent 5 from turning into a 1, and the good kind of 1 which is actually bad
A sump is simply a way of utilizing an overflow which allows for surface skimming (organics float) sending what needs to be filtered to the skimmer more efficiently. It cleans things up a little providing a place for equipment and allows for larger equipment like a giant skimmer to be used.
For me I try and keep things simple, 1, 3 & 6 results in what I believe to be the best ration of good results to low maintenance.