Jacks are aggressive, so in a 75g you could have a pair but I'm afraid not much else. Bristlenose or some smaller dithers like giant danios. They are very territorial and a 75g doesnt offer alot of real estate. A pair would be very cool in my opinion. If your considering another tank and from your posts you have a passion for big and feisty cichlids I would consider a 6ft tank if possible.