Could be an issue with lighting or ferts. I'm not sure what a "twin compact" is, or how good the reflectors are. Also, fishload is important, as a lot of fish will create a lot of poop, which will limit the need for additional ferts in a low-light setup.
With the number of plants you have, I'm going to guess that you don't have enough nutrients in the water column. Infesting in some liquid or dry ferts (NPK + Trace) will probably help you out. For more specific advice, you're going to need to be more specific with both your lighting and fauna.