Hello Andrea. Thanks for posting your questions here.
On FB, I suspected you had an issue of cross contamination and you have confirmed it. It's good you have placed them in a hospital tank.
At this point, I would recommend upping the salt to around 8-10 TBS per 10 gallons for 3-5 days, replacing the salt removed during water changes. I would also increase your water changes to 75% per day. This will help reduce the pathogen count. Since you are on well water, there hopefully won't be much of a ph swing, but if there is then you should age your water. I also don't think RO is necessary unless there is a specific reason you use it. Discus are perfectly fine with most water supplies, even hard ones. Since you already have Furan 2 on hand, I would use this according to directions as well. Since there appears to be an external fungal or bacterial issue, I would keep the temp at 82. You said your Nitrites are at 5? Are you sure this isn't Nitrates? If there are nitrites in the water then you have a filter cycling issue.
Here is a very similar issue going on now that you may be interested in http://forum.simplydiscus.com/showth...es-Please-Help!!!