weird loss of multi

[rfb]

I have lost three multipunctus in the last few weeks,and the weird thing is that they appear to be in perfect health.They have no change in behaviour except that they seem to swim slower and one had a bit of a red spot on the area just before the tail fin.I am not sure what this all might be but it is sure frustrating as they are cool and not cheap.The tank mates have not changed the only notable changes there are the fueleborni spawned and so have the auratus both males have been active but nothing else.has anybody else had something else like this or anything that might help save the last one if this starts to happen.