Tank Crash - Fish Breathing Heavy..

[Pinchy]

Hello all,

I require your help. I attempted to move my 55 gallon to my new house where i had an empty 75 gallon bowfront setup. I had premixed saltwater two days in advance (30 gallons) I have moved all of the water and LR into the new tank as i wanted to keep parameters as stable as possible. Before introducing the fish I waited for the temperature to match the holding tub the fish were in, then started the acclimmation process. I then added the fish and they were fine for the first night. The following morning i noticed the fish were respirating heavily (over 100x per minute) particularly my Yellow Tang / flame angel. The yellow tang has now passed away... This is the first SW fish i have had die since starting the hobby a year and a half ago. It is a very sad day. The yellow tail damsel, cardinal and sandsifter goby are attempting to eat, the others show minimal interest.

I am stumped as to why this happened. The only thing that i have changed is added a Fluval 304 with fresh filter media to remove the floating particles.

in the filter is Floss, Carbon, Bio Balls & GFO.

Parameters (tested when i introduced the fish two days ago & last night):

Ammonia: 0
PH: 8.2
Nitrite: 0
Nitrate: 20

The only thing else to mention is my sump / skimmer hasent been online the last few days as i need a few parts for it before i can get it running. There is a TON of surface agitation with the 304 and X3 Koralia K1's pointing up at the surface.

PLEASE HELP i do not want to lose anymore fish. Is there anything i can add to the tank in terms of additives?

Thank you for your time.