Things drop into place...
Your coral issues now make more sense now Ive twigged that youve just moved everything around.
I remember that you have just bought alot of new rock. It goes without saying that this would have in effect caused the tank to do another cycle. This inturn will have caused ammonia and nitrate spikes, both of which will cause your corals to die. You should never remove rock work in that amount and then expect the tank to run the same. Even with the same sand etc there will be a full a cycle. Even when adding 10kg of new rock to my existing set up that already had 80kg of rock in it I noticed a spike for a few days as stuff dies off the new rock!.
With this in mind if you have anything left in that tank with regaurd to coral I would take it out ASAP, as the problem will not solve with water changes. You need a bucket of aged tank temp salt water to rinse the corals off before you add them to the nano. Anything that is looking like its a gonner should be just thrown away as dying corals release toxins which will kill and stress other corals.
The coral in the pic looks verry stressed but still alive. I would rinse off anything thats loose then add to the nano.
You now have to recycle the big tank. Lots of water movement and surface airation will help with that.
Its always best on here to give a full break down of your issue so people know whats going on, as we dont always get chance to either read all the posts or match different topics together to make a full picture. If you had explained the situation from the first post then people could have advised you straight away and maybe saved more
Just to point out that you must keep a close eye on that main tank If you still have fish in there, then they will deffo be strugling and adding fish food to the setup to keep them alive will only make the cycle worse and last longer, thats if the fish survive. You need to get a tank from somewhere and get them out.
Others may jump in here and give more advise .........................