defo worth getting a bigger tank, if he isnt stunted too badly he will put on alot of weight with every half inch... a 13 inch o is massive! i have kept many cichlids inc o's and i was surprised yesterday when i put my new jag of 11 inch in my 300g community with a 9 inch jag, its easily twice the weight, get something with a 2x2 dimension side on imo.