Are my bta's dying?

[irene060606]

I have a 14 gal nanocube deluxe. With 2 clowns, 2 baby bta's, 5" bta, and hermits. Lighting is stock. Levels are great and I just did a 20% water change 2 days ago. I'm a newb but the tank has been running for two years. I have had the big bta for 1 1/2 months now and it was thriving. About 5 days ago the 2 tiny bta's closed up completely. The large bta has reduced in size by 3/4. It has thined out ALOT and closed up almost completely. It is not letting the clowns host at all and has moved out of the light. A week ago my cleaner shrimp also died for no reason. How do I deal with this with my tank not taking a beating? When lookin at the attached picture please keep in mind the clowns are babies and the bta was EASILY 5 inches across. Now its less then 2. Are they dying? If so what do I do? PLEASE HELP