Some pieces really surprised me.They looked like they had disappeared and in a few weeks they were coming back.Others,came back relativly quick.Have these been in your tank long?Mine were already established before they died back.I don't know how much this played in thier making a comeback.If you have a healthy system you should have some pretty good luck for some to come back.I'm no expert though,and things differ for each tank.Hopefully you will be ok!