I've tried to keep those little cats 3 or 4 times now, starting with them at all different sizes... and I can not keep them alive. They always start off eating fine, then begin eating less, and finally die... I don't know how to make them last... and have done WAY WAY too much research on the damn little buggers...
I also always have a bit of salt in my tanks, but I did try brackish with a pair once... and it didn't help...
Oh yeah, and these were the only fish I have EVER had issues keeping. (and I have a 4-line cat, raphael, sun cat, and ID shark along with some polypterus and frontosa and a bunch of other cichlids...never had problems)