It's 5 discus in my 75 gallon tank. 3 stay together, and two kind of stay seprate from everything (they swim alone, single). I have tried all that I have. Flake, colorbits, discus flake, brineshrimp, artemia, rotifers, beefheart, tubiflex worms, and bloodworms. Plus I think I remember using some plankton and mysid shrimp as well as some other marine flakes. Every other fish eats anything I add in the tank, but hte discus never eat.
"2 kind of stay seperate from everything (they swim alone)" These are most likely the most troubled of the 5. Seperate them to other quarters 29g or bigger and raise the temp on them to around 98F(over a 3 DAY period). (trust me these fish can handle high temps just fine with "HEALTHY" "CLEAN" "WELL OXYGENATED" water). Plus the added temp will shorten the lifspan of the bacilli or virus. Add some bacterial agent to the food as just putting it in the tank will not fix anything, and probably make the bacteria immune the drug. The drug I would use would be a wide spectrum antibacterial following the recomended doses on the package "TO THE LETTER".
Secondly: How do their stomachs look? Are they very plump around the anus area or midsection at all? (compared to normal) If so this could be an internal virus problem with a secondary bacterial infection. Again seperate them and give them the best treatment possible for virus (bought at an LFS). by soaking the food like Tubifex worms for a few hours in COLD running water, then leaving the worms in no water and adding the medicine to the worm container, and feeding within a few minutes you'll get some med inside the fishes stomach if they eat at all. (Normal Tap water carries antibacterial for human consumption and will kill any bacteria of note in the worms).
If the fish are truly not eating with the higher temp and medicine in their new tank then they might be beyond help at this stage most discus that are not eating at all and will not accept worms even, simply have no way of combating what is wrong with them and they will most likely die. This is sad of course.
Thirdly: What are the other params like? ammonia, nitrite, nitrate, PH, and DH? Have you tested these yet?(if any are way out of sorts compared to whats expected for your tank then this could be a partial cause to your fishes problem). These params by themselves probably will not keep Discus from eating but they do have a tendency to make the fish VERY STRESSED.
Forth: What about water changes? (I recommend at least 90% daily for the whole treatment) Also how many other and what types of fish do you have in with them? Are there any aggresive fish in the tank or at least something that perhaps has the ability to out-eat the discus who by default are slow to be the aggressors in food battles. Angelfish or other cichlids might be out competing them. Again the seperation of the two fishes most likely to be failing might solve this arguement.
If all else fails try to keep the sickest fish away from the others for as long as possible and see if the 3 remaining get any better. Might be something with the 5 not grouping together but this is pretty unlikely.
Also Tubifex worms will stay in the gravel for very long periods of time henceforth your discus might just be to full(but then you should see some sort of feces).
I have had many discus over the years and bred them for many years back in the 80's and 90's but I have had something like this happen only a couple times and it was cured with the higher temp and massive waterchanges and wide spectrum antibacterial and Virsu agents ued at the time. The only other way my discus ever became dark was at breeding time(but they still ate) and then they just needed a place of their own.
Hope some or all of this helps as I really hate it when Discus aren't having a good day!