I would give the fish a day and monitor for any other symptoms. Since it is only 1 fish, adding other fish to aquarium may have stressed it and it was a weak fish to begin with. That would be the best case scenario.
Also, keep close eye on other fish.
If columnaris, kanamycin and nitrofurazone would be the treatment.
But, give it a "wait and see".
Thank you Amy.
I got up earlier than usual to check on them. One of the gourami has died. Body still intact, looks like the shrimp hasn't had a chance to get to it yet. No outward signs of how it got done in.
The other gourami is alive. Will be observing him. They are very shy fish and I guess since he's the only sparkler in there he might become even more reclusive but fortunately he seems to be doing fine so far. No clamped fins, no difficulty swimming.
The corydoras are all accounted for and are doing normal cory things... I'll be keeping an eye on them for the next couple of weeks. I guess I'll be doing yet another unplanned 50% water change later today.