Both blues and opalines are color morphs of the three-spot gourami, trichogaster trichopterus, as are golds. All are known to be semi-aggressive. You might distract the males with a few females (I do a 1:2 ratio, m:f), but, in a tank that size, some line of sight breaks and hiding places might help, too.
2x20-longs, one heavily planted. Platy rancher. They. Won't. Stop. Breeding.