Hello, I have 3 dinosaur birchirs(7 in.) an needlenose gar(10in.), a pleco and angelfish(5in.) and 2 jack dempseys(6in.). I know jack dempseys are said to be alone in a tank..... I think mine are both males. I just bought them at the pet store today and was wondering what problems I might face? And other possible tank mates? Thanks,Alex