Hi Created. Can you describe some of their behaviors? Do they dart and rub on things? Will they eat still? Are they lethargic or do they clamp their fins?
Without that info, it's hard to make even a semi-accurate diagnosis but there are a couple of possibilities and a few things you can do in the meantime.
The possibilities are external parasites such as flukes or costia or the beginnings of columnaris. Either way, the best treatment would be to give them a salt bath for an hour. I'm not too familiar with oscars and how well they tolerate salt but I'd say 1 tsp per 2 gallons OR whatever the directions on the packaging say. If they show no signs of distress, you may want to increase the dosage. Because your tank is so big, I would definitely recommend carrying out this treatment as a bath in a hospital tank.