what are common reasons for rapid clam decline?

[greystreet41]

I've had 3 squamosas for several months now and 1 of them is literally dying before my eyes as the evening goes on and I have no idea why. All water parameters are fine. The only thing I think that could be happening is that my flame hawk often perches on them...could that be an irritant to cause death?
thanks

 

[mbbuna]

can you please tell us everything about your tank.
how big?
how long has it been up?
what lighting?
what fish?
what do you feed?
please list water parameters.
and a few pics would help