Sounds like bacterial infection. Try not to use any meds. Meds heavily deplete the water of oxygen, which is already depleted at high temps. If anything increase your temp even a little more, like say 90 and add an airstone or powerhead. Also, make sure your using a good thermometer, like a internal glass tube thermometer or better yet, a digital thermometer. Next step, check your water parameters. Largely, look at your ammonia and nitrite levels. Quaranteen tanks often don't have large populations of nitrifying bacteria. One way to add large amounts of nitrifying bacteria is to add something to the system from a fully established aquarium. Filters and large decorations, namely wood, are excellent for this. Best of luck to you.