So I sent the fish back to my LFS and they said that they'd try to treat him for 7 days and get back to me. I really hope he makes it.
However, based on what I read, I don't think that ts columnaris. it's been 2 days since I took him out of my tank and the remaining fish seem to be doing just fine. The second pearl gourami (female) looks to be doing better than ever (eating well and active).
I did a 50% water change after I took him out of the tank anyway. Would any of you recommend I add anything else to the tank? Maybe some kind of medication to prevent further diseases?
Treat with kanaplex as directed above.
The truth is that I decided against doing anything myself since I dont have an adequate quarantine tank and, quite honestly, im afraid of adding anything in my tank that would affect my filter or system...