ok sooo you are def still going to need that 220 if you plan on keeping that RTC for a little longer, and obviously you dont know that this still will not be nearly large enough to keep it for life, also the diet you are feeding them is absolutely horrible, im surprised if they didnt get HITH if they didnt have it already, im sorry for your loss it sucks losing a fish but in your case it was inevitable, get your remaining oscar off of those horrible feeders and onto a good balanced pellet, also you shouldnt be feeding beef that often (if at all) it just leads to problems down the road since they cant digest that kind of meat properly, PLEASE PLEASE do more research and actually take to heart the advice that you read on here, if you absolutely have to feed some type of feeder as a treat then stay away from those parasite riddled store bought feeders that are extremely unhealthy for them anyways and feed them some of your convict babies or something, or just do insects and what not.
oh and that beefheart and everything is also very bad for water quality which you are already having issues with, you should not let your nitrates go above 40, better is to keep it below 20