I have single male synspillum, bifas, and fenestratus between 8 to 12", and an 8 inch Green Terror and a few smaller fish in a 125 gal. They get along well and have established a peaceful pecking order. I have a zero sum game plan in fish keeping, and only add fish to replace fish I lost or sold. So I have no plan to upgrade into a bigger tank to accommodate more species I want. I do have a few 75 gal to move fish around if I run into aggression. If the fish cause too much trouble and I can't manage its aggression, I will just get rid of it. This is why I only raise one Festas to see how it can fit in. I normally keep only a single male of each big CA species to avoid paired up aggression, but Festas female is so pretty that I don't mind it turns out to be a girl. But I read that Festae female meaner than male.