I've got a 75 gal. tank, doesn't even have water yet. We're in the process of rinsing all the rocks and stuff, so I thought I'd do a little research while we wait. I keep seeing you guys talking about all these kinds of filters and so I'm wondering what kind of filter should we have? We don't have a lot of room for the hang on penguin filter thing that my husband got and I was wondering if there's a better option. We're going to have a school of Cardinal Tetras and 5 or 6 Discus. I know NOTHING about filters so if you could help me out I'd really appreciate it.