If the injury is anything more significant that a slightly nipped fin, you want to put the fish in QT. A separate 10 gallon will be great for that.
Chances of 8 oscars living long term together in a 220 is slim to none.
Definitely wise to run two lower wattage heaters over one higher wattage. Either that or run one higher watt unit plugged into a temperature controller.
I'm trying not to get excited...
24 hours hours after last WC 50%.
Please see those first tests my readings are -
NITRITE - 0