Good morning Craig...
I'm "old school" when it comes to water keeping, so never use chemicals in my tanks. Fish ailments are difficult for us amatures to recognize, so I'd recommend an aggressive water change schedule to start. For the next 10 days, I'd change half the tank water in your tank or tanks every other day. You can also raise the temperature in the tank a few degrees, 80 should be sufficient. Maintain that temp for 10 days.
Lastly, I would add a little standard aquarium salt to the water change water. I've used a teaspoon in every five gallons of my water change water for several years and have never had a disease in my tanks. Most fish pathogens can't tolerate even a trace of salt in the tank water.
Whatever is wrong with your fish, a little warmth, aquarium salt and a lot of very, very clean water will help.
Please keep me posted if you like.
"Fear not, my young apprentice. Just change the tank water."