Glad you posted the pics. It gives us a better idea of some of the problems your GBTA might be facing....
- my experience with a GBTA and an RBTA are that they don't like very much water movement. Placed where it is, midst your SPS corals, it may be getting too much water flow, and may be staying in the safety of the rocks to stay out of the excess flow. Don't know if you have lower water flow areas of your tank, but if you can move the GBTA to such a place, I'm sure it would appreciate your efforts. The easiest way to move a BTA is to move the BTA and the rock it's attached to.
- how often is the GBTA getting fed and what do you feed it? Mine get fed every 2-3 days with thawed frozen mysis. The larger the BTA is, the more mysis it gets. Here's a video from Jan 26/06 of my RBTA being fed....
http://www.lostmymarblz.com/v-rbta-f...s-ja-26-06.wmv
HTH
