Can you please provide a total stock list for your large tank? Not what is in there now but what was in there. It sounds like you had two aros, a TSN, some plecos, and maybe something else. With all of those fish and the fact that you are feeding beef heart, which is a very messy food makes me think that your nitrates (and probably TDS) are up pretty high, which is not good for the fish. I'd recommend taking some tank water to the LFS so they can test it. Almost any of them will test it for free. That will help us figure out where your at right now.
Also, so that we have a wholistic picture, can you update us on all of your tanks and what is currently in them? This will be very helpful.