I'm sorry but I have to agree with tlindsey and FJB, the aquarium is too small for all those fish. I also agree with FJB saying the water test should not read 0 nitrates. As well as kno4te saying the Oscars eyes look to be damaged, possibly the Oscar scratched his eye.
As for the Parrots if they where free of black markings and they developed recently, that's usually a sign of stress in parrots and generally associated with water quality in my experience. Are any of the fish flicking/flashing trying to scratch themselves? If you had an ammonia spike it may mean the tank isn't properly cycled or a mini cycle was started by adding fish or overfeeding that increased the bioload. The water also looks cloudy hazy which maybe a bacterial bloom which would be a visual representation of the imbalance.
As for the Parrots if they where free of black markings and they developed recently, that's usually a sign of stress in parrots and generally associated with water quality in my experience. Are any of the fish flicking/flashing trying to scratch themselves? If you had an ammonia spike it may mean the tank isn't properly cycled or a mini cycle was started by adding fish or overfeeding that increased the bioload. The water also looks cloudy hazy which maybe a bacterial bloom which would be a visual representation of the imbalance.
