a 50 gallon tank for now is plenty of room for a shark. even a 20 gallon long would be good for a shark for right now but your going to have to make sure you upgrade his tank when he grows. I got 4 shark eggs now in a 29 gallon thats ready to hatch any day now I have been holding onto them for almost 3 months. As for the filter. you can use anything really. I been using the new cascades 200 and 300 model but if your going to filter a 50 gallon I would go with an emperor 400 which you can buy them online for like $40+shipping