Apologies, clarification: I have filters running with no carbon inserts and just foam due to metroplex/sulfaplex treatments. There is a submersible filter providing surface agitation for oxygenation in this quarantine tank. (See pic)
Gasping began when the fish was brought home, not a new development nor changed with adjustments to filtration and treatments.
Second pic is how it started, third is how the area progressed over one week.