I just got the pm, and just finished reading through everything in this thread.
My opinion, it sounds like an ich outbreak, starting slowly but escalating quickly. The white spots, the scratching, the loss of color, the heavy breathing... all an indication of the parasite.
While the Formaldehyde in your meds is safe in lower dosages for neons, the malachite green is not. The preferred method of treatment for something like this would be a medication called Formalin, which is just Formaldehyde... but it is only going to be safe for neons at 1/2 the suggested dosage. (suggested dosage is 2 drops per gallon, you'll want to use 1 drop per gallon)
I would suggest treating the qt'd fish in the quarantine tank and waiting until everyone is well again before moving it back to the main tank. You'll also want to add an air stone to the main tank during treatment because Formaldehyde will use a fair amount of the oxygen in the water. I wouldn't worry about the 10 gallon with only 1 fish in it, but the main tank has quite a good size population.
Stress is your biggest issue. The stress of being moved, the stress of a new tank, the stress of 5 more coming into the tank after only about a wk...stress from medication that may or may not have been safe... Neons are prone to stress related illnesses, and ich is usually brought on by stress because stress weakens the immune system, which causes an inability to fight the parasite naturally.
Also, 78 - 80 is the temp I would be suggesting for keeping neons. If you get too cold, again you compromise the immune system.
Best of luck to you, and if you have other questions or concerns, please ask away. If you should notice any new symptoms, please post them asap.