Bullheads like to be in schools, so get four or more. I have four bullheads, and they've shredded my vals but left my water lily alone. I'm getting some new American vals, so hopefully those will grow better because they are more tolerant of cold water.
Also, if you are looking in to making a biotope, why not add some native plants? American vals, anarcharis, hornwort, water lillies and cow lillies are all commonly availible native plants, and they're all relatively easy to keep (sorry, I couldn't help but suggest it - I really love my aquatic plants).
Then maybe have a sunfish or two, or maybe a school of minnows? They're active and readily availible at any bait shop.