You say one of your cory's doesn't look good. What do the barbels ,or whiskers look like on other cory's? I have found that cory's nearly always do better over sand substrate. If the grain size of gravel is large or has sharp edges as opposed to being smooth,then over time,,the fishes barbels can be worn down from their constant shuffling through the gravel in search of food. Once the barbels or (whiskers) become worn down to nubs, then infections can take place.
Up until this weekend I had been keeping eight Julii cory's in a 56 gal with small smooth gravel. Before this,they were on sand bottom 29 gal. I moved them back to the sand substrate this weekend cause I noticed that nearly all of their barbels were nearly nubs even though my gravel was smooth and rather small grain size.
Your water parameters sound good and were it me,I might consider setting up a tank if possible with sand substrate and placing the fish there. (after the tank cycles)
Keep those water parameters up and fish will have a good chance of healing. If the fish does not get better,I would euthanize it rather than treat the whole tank for unknown illness.
I have doubt's that the Angelfish is the culprit and do not know what Goldie's are. If goldie's are chinese algae eater,,then there is your culprit. These fish are actually poor alagae eaters and become aggressive as they mature. Hope some of this helps.