Evidently your LFS staff don't know the requirements of Discus. Concientious retailers would not have allowed you to get Discus in the first place with your current stock...
The bala will get to 18 inches in captivity, but Chester Zoo apparently have some at 3ft length. He is not suitable, and needs to be removed.
Considering how little advise you have taken onboard here, I'd give your Discus about a month to two months to live at most
To be blunt, and to give you a quick current situation review from how I see things from my end, ATM, going by your current resposes so far, I can see you are likely going to fall into one of two categories; "too ignorant to learn" or "more money than sence".
So far you have lunged into every purchase without doing any research and you have ignored the advise of members on here. Then, and only then, you wonder why things aren't working for you. Try a new approach to keeping fish, where you make no "spur of the moment" desisions in the LFS and you will get far further.
Seriously bud, you need to research before buying. If you don't, you will loose fish. You're LFS has proven they cannot be trusted, so you need to take all their advice on the matter with a pinch of salt
All the best
Rabbut