Well I've just this week noticed some of my larger/older shrimp have this ring. Some that I recentky moved to a new rank and now one in my original colony.This is something I was told when my shrimps died, it may or may not be true. But if it is true any bacterium only affects one species of shrimp. My first shrimps all died with a white ring but since then I have had no problems; not the ones born in my tanks or the odd one.s I've bought to 'increase the gene pool'.
Could be more as I have a pretty nice colony of RCS.
I also have 2 Amano; tough as nails!
I almost forgot ~~~~~~~
So, okay, someone told me today fruit flavored tums helps. Sceptical.