fish dying

[Darkness]

my dwarf gourami that ive had for 3 weeks just fine is dying. its at the bottom of the tank partway on its side. it goes up for air every once in a while. Its feeler things on its underside are less that an inch long. they used to be 2 inches. tests show 0 0 25. The only new thing in the tank is a pleco i put in last night. could he have caused this? I have him in quarantine but that probably wont be enough. what should i do? I have melafix, should i add some of that to the quarantine?

[sergo]

i didn't have any luck with my dwarfs and have heard a lot of people say they haven't either. 1 of mine died for apparent reason and 2 others developed what i thought was hole in the disease and they didn't make it after almost 2 weeks of treatment. i won't be getting anymore of them as they seem a little shady. my honey gouramis are just fine and have been since day one. must be a breed thing.

[cocoa_pleco]

i havent had much luck with dwarfs either. when i had a 20g planted set up, i had a dwarf in it. My blackshark has a habit of chewing on floating corpses, and sure enough one day i found him chewing on the gourami. i was bored, so i chucked the corpse under my microscope, no parasites or anything