I've had some established chaeto in my sump for many months now. I've pulled tons of it out consistently on a weekly basis. I also had a major aiptasia invasion in my refugium. I'm talking hundreds and hundreds. I added 6 peppermint shrimp and within two weeks they're all gone. Amazing! Yet the strangest thing happened - my chaeto suddenly died. Just lost color and started melting away. It's been going strong for a very long time. It has flow. It has light (Kessil h380). It has iron dosing. Could it possibly be the introduction of the peppermint shrimp? Is that even a thing?