if the difference was too great the blakc would kill the lei or vise versa, but leis are ALMOST as aggressive as Jars imo, and shud be treated as only slightly more comm. safe. not only that, but most aros dont get along neways unless theres like 3+. so id just be safe and not do it.
if more people hed felt compelled to answer this question the replies would have looked much the same as in the "silver with jardini" thread floating around this one somewhere.
Leis are a very weird fish.As far as aggression they are not bad at all,they will get along with most any other fish just like a silver...but there is a catch.
Leis hate anything that looks like another aro.I'm not talking looks like another aro to you,I mean looks like another aro to their tiny brains.this means anything silver is out.heck,anything shiny at all is out (my lei can't even stand my snook).
anything with a light grey color is often open for attack as well.
I can count on one hand the number of times I have seen a lei combine with another aro and all those people have massive tanks and more than 2 aros.I would still be able to count on one hand the number of times Ive seen it work if I lost 2 fingers....