My name is ***** ***** I have been a Vet tech for 30+ years and a fish keeper over 40 years.
Have you checked the water parameters?
What is the Ammonia, Nitrites, Nitrates and Ph?
What type of test kit are you using?
I do not have a test kit. I usually take a water sample to fhe local aquarium to be tested. The last time I did it was fine. Plus like I said I just did a major water change.
Major water changes can cause new tank syndrome and start the nitrogen cycle over causing ammonia spikes. 5 discus is a 55 is a lot and I suspect you are having a water quality problem. I suggest getting an API master test kit to check the water. We need the Ammonia at 0, the Nitrites at 0, the Nitrates at 20ppm or less and the PH at 7.0. Any time we add fish that will change the water parameters. It is so important to use a good test kit like the API master test kit to get a good reading the strip type can be off. Right now to try and save the fish he should be in a hospital tank until you can get teh water parameters regulated. Start with a 25% water change and add one teaspoon full of aquarium salt per gallon of water. This will work as a tonic in the tank. Do this one time and when doing changes only add enough aquarium salt for the amount of water taken out to go back in. I think if we can get the water parameter correct, it will make a huge difference in the tank and the fishes health. http://www.firsttankguide.net/newtanksyndrome.php