I have an agressive male jack dempsey. He is about 6 inches and used to be housed with a 10" clown knife until i had to sell the knife because the jack was beating him up. The jd is in a 55 gallon and I was wondering if i could get a tankmate that would be ok with him. If i upgrade it will only be into a 75 gallon scence i don't have the clown knife any more. If i still had the knife i would have been getting a 150 gallon but don't need it any more and want the money for other things. I'll post pictures by tommorow!