Help! Fish breathing heavy, loss of appetite

[Spyd]

What is your alk level? It may be very low. Have you been dosing alk or a ph buffer at all?

Putting the whole tank in hypo was a little drastic IMO. If only one fish had ich, I would have just left it alone and fed some garlic puree with the food to boost all of their immune systems.

How long have you been in hypo for now?

[MitchM]

If that tank was put in front of me right now, I would remove fish that are showing signs of ich, along with some of the hypo tank water into a separate qt tank.
I would then start slowly raising the salinity of the display tank again.
The hypo is stressing out your currently healthy fish.
Find that missing chromis.