Again, let me be the first to say welcome to PB. The rest of these guys are so smart that they get right to business before sayin hello. I'm not near so intelligent but have a suggestion. Since you have a relatively small area you should consider and research aerating and bacteria treatment. With a DIY air system and homemade bacteria I think over a bit of time you should be able to accomplish your goal and provide a better envorment for your "MAJOR" fish.
Good luck, Bob-O

Do nature a favor, spay/neuter your pets and any weird friends or relatives.