Your 75 is 18 inches in width right? If so, then yes he will get 14 inches if it's a male, and you stay consistant with your 50% water changes. I'd really offer a more variety of food, and I really wouldn't feed beef heart too much. I'd mix up some frozen krill, brine shrimp, mysis shrimp, bloodworms, some frozen spirulina and some of those high quality "Ocean Nutrution" brand frozen foods. Even if they are for marine fish, don't let that fool you and always check the ingredients. Their "Shark" formula is one of the best frozen foods for Rd/midas IMO.