Hi Kristen,
From the questionnaire, I can't really see what might be the cause of the problem. The pH of 8.3 may be on the high side for that particular fish though I think that members here have kept fish in that range before.
You have done well by removing the fish to it's own hospital tank where you can treat it and remove any social stress.
See Ksermie's thread on a "Very Sick Discus." Brian outlines the use of salt which might be your best bet, a little salt, pristine water and some rest. Once they go dark, it is an uphill battle. The hospital tank is your best bet.
Beat of Luck,
I hope he/she pulls through for you,
Andy