It's not a good idea. I would either get rid of the aro, or buy a tank with at least a 300 gal. capacity. That aro will jump out of that little tank, or hurt itself trying to in a few short months. That's what they do if they get cramped and stressed. I got a silver aro at 6 inches. It was in a 240 gal. for 10 months, and grew to 26 inches with power feeding. I sold it to a guy with a 600 gal., because it had darn near outgrew my tank! Anyway, that 75 would make a good tank for small group of discus, but not both.