No matter, its largely agreed that iodine dosing produces no real affect. It is also devilshly hard to test for and in my experiance with actually dosing it for the better part of 6 months I can say from experiance that it had no affect for the good or bad with my tank which is heavily stocked with inverts and a few brains. I have been using IO for a few months now as well and was using seachem reef crystals before that. I have seen nothing detrimenatl with that change either. ca,mg,ph and alk all stayed withing nsw params with mg being a bit lower with io. True that iodine dosing may not be dangerous but it is largely useless. I would go with phosphates and overall lack of trace elements due to prolonged water change intervals being the OPs issue with the brain.

All that said,this is directed to the OP. Have you changed the flow in your tank in any way in the past weeks? How about lighting changes? brains do not do well with hard flow or high light if its a rapid change.