How often have you attempted to feed, and when was the last time it actually took the food? I read a lot about feeding BTAs anywhere from every 3 days to every 7, but everytime I have tried to reduce my feeding schedule to even the 3 day mark, my BTA has nearly died (a starving BTA will lose size and the tentacles will gradually get shorter and shorter until left with only nubs, and counter-intuitively, it will lose its feeding response). I feed mine daily, which it eagerly accepts. I have also had better luck feeding mine
krill than silversides, though certainly the majority of posts I have read concerning food do use silversides. I may just be experiencing differences of an individual speciman. A pinhole sized mouth opening is not really a concern. Wide enough for your pinky may or may not be...what was going on when you observed that, and how long did it stay open that much? It would be normal for the mouth to open when deflating or excreting. I have not kept cleaners with my BTA, but have read that it is normal for the shrimp to try and steal food right off the
anemone, which may be what they are doing or at least trying to do. I am a little worried about your lighting...compacts are typically not considered intense enough for anemones. What is your daily lighting schedule?