I think a 90 is way too small for a lunare, they are extemely active fish and any new addition to that tank will be harassed big time. I have one for about 4.5 years, he started small about 3" in a 100 gallon he is now 8-9' in my 500gallon, beautiful fish with lots of personality, but can be quit aggressive in a small tank, in my 500 he shows little aggression towards anyone now.