Gourami with digestive issue

[CopperCake]

Hello everyone. This one's got me stuck. I've lurked around forums like this before and thought maybe someone would have more insight then I do.

Concern:
I just moved my male tiger gourami into a new(cycled for a week) tank. He did well on night one, but the next day he was suddenly colorless and lethargic, then started expelling bubbles from his gills and his vent.

My Theories:
Doesn't seem like a puncture or swim bladder issue. He swims fine when he wants to.
I called the person I originally bought him from who suggested it may be bad food rotting in his belly and releasing air. He only eats one kind of flake food. I offered frozen bloodworms for the first time a few days prior, which I did not see him eat. However I think that theory might be likely.
I'd also like to mention the night before he moved tanks, I've been doing a preventative round of melafix and primafix, wasn't paying enough attention, and accidentally poured primafix directly on him. He may have thought I was feeding him and may have injested it. Never seen any ill effects on guppies when they swim into medication, but I'm unsure with him.

Current treatment:
He's been medicated with furan 2 and aquarium salt for 2 days. Furan 2 didnt seem to have an effect, but aquarium salt seemed to help some. Still overall lethargic, and I'm not sure what to do.

Any advice or ideas would be appreciated.

 

[Delapool]

I’m not sure if related but have bumped off a few fish using melafix/ pimafix that were otherwise healthy. I’ve found (and only an imo) that these should be well mixed into tank water so fish don’t swim through a ‘cloud’ of it.

I can’t find any evidence they are particularly more dangerous for certain fish.

 

[Aiken Drum]

I’m not sure if related but have bumped off a few fish using melafix/ pimafix that were otherwise healthy. I’ve found (and only an imo) that these should be well mixed into tank water so fish don’t swim through a ‘cloud’ of it.

I can’t find any evidence they are particularly more dangerous for certain fish.

Whenever i add anything into the water, i either mix it into a bucket of water and do a 10 litre water change or dose it into the stream of water leaving the filter so it quickly mixes.

 

[CopperCake]

I’m not sure if related but have bumped off a few fish using melafix/ pimafix that were otherwise healthy. I’ve found (and only an imo) that these should be well mixed into tank water so fish don’t swim through a ‘cloud’ of it.

I can’t find any evidence they are particularly more dangerous for certain fish.

I do worry this might be the case, and it was entirely my screw up if so. Is there anything I can do to help this situation?

 

[Delapool]

Water change was all I’ve found. Hopefully comes good.