there are many things that can cause this... ranging from not enough water flow to parasites, etc.. could you maybe describe your system? what stuff you got? is anything else doing well? filtration, water flow etc.
BTW, just because you can't see any parasites/host or predators of any kind, doesn't necessarily mean they aren't there, trust me. Just provide as much detailed info as possible and maybe a pic or two and someone here will gladly help you my friend.
How long have they been in your system? How long have they been closed? When is the last time you moved them? How old is your system? Are they colonies or is it a frag. When you say all how many do you mean?
It's hard to say why without knowing a bit more. How are they doing now?