Not sure why you would wish to fresh water dip it, as I dont think it would help this problem. However not an expert on them. Tried one or two a way back when and they receded. Some think many of the plates should be left unharvested because of the problems keeping them.
Aquarists that I have seen with success in keeping them attribute it to feeding. Wonder if you tried something a bit larger like a piece of krill or perhaps even a piece of silversides or whatever those minnows are called.
Have a friend who,s had luck and will ask him tomm. what he suggests.
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Doug
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