I have been keeping sharks for 20 plus years. I have always had good luck with a wet-dry filter and a quality protien skimmer. Sharks require high oxygen levels. A wet-dry produces much higher oxygen levels than cannisters and fluidized sand filters. A good skimmer will also reduce the load on the filter and help out with the oxygen levels. I would always suggest oversize filtration with sharks. If money is an issue, you can easily build them. I have one built out of a large rubbermaid tote filled with bio-balls (you can use plastic pot scrubbers if on a budget) sitting inside of a rubbermaid trough. The troughs come in 75, 100, and 150 gallon sizes and can be purchased at a feed store or tractor supply. You can easily drill your hole for a bulkhead to connect a pump. You can use polyester batting material (buy at a fabric store) on top of your drip plate or under your spraybar for mechanicle filtration. It works the same as bonded blue. I would recomend buying a good skimmer though. I just bought a Bashsea beckett skimmer and it is the best I have ever used. good luck