with such a large selection of stock it will be difficult to work out who the culprit is. How does the Undulatus behave both of mine in the past have been extremely aggro but ofc the aquariums were nowhere near the scale of yours.
Not the lion I think we can rule him out along with the eels, if the culprit is the fish I think it may be one of the triggerfish as some will bite fish such as butterflies and angelsI want to say the lion fish... or the eel that is in the pic of the dead angelfish
But I really am leaning towards the lion fish... Put him in a small quarntine tank and see if he deaths continues
Not the lion I think we can rule him out along with the eels, if the culprit is the fish I think it may be one of the triggerfish as some will bite fish such as butterflies and angels
Can I ask why you think we can rule them out? They are predatory and aggressive especially the lion. I still think he should take the lion and put it into a different tank and see if it changes or not... I may be wrong or I may be right but it doesn't hurt to try... (Unless the lion stabs him cause that would defiantly hurt lol