I've had this same awful experience with some of my ricordea. Three of them just completely disappeared today. Vanished. I was sure something was eating them. The ones that disappeared are newbies -- in my tank less than a couple of weeks.
The other weird thing was that one of my ricordea that's been attached to a rock for over six months detached today. It seems too 'coincidental'.
I did a freshwater top off today, my salinity was at 1.025 before and 1.023 after. Could this be the cause?
After I found them missing and read this thread, I did a 30% water change (30G aquarium), and ran some carbon. Is there anything else that can be done? I have about 50 ricordea in total and am REALLY scared I'll lose more.
....all this once I decided to convert my nano to all ricordea because I'd always had good luck with them. <sigh> is nothing easy?
I'd really appreciate more feedback on this.