I want to build a quarantine tank for new fish, but I am not sure of the best way. I think I want to use a large plastic container (something with high sides to deter the predators). I already have an aerator. What kind of filter do I need? If they are only going to be a few fish in it for 3 weeks, maybe I do not even need a filter. How do I know if I even need a filter? Do I need anything else?