Also this is from Anibis (hope I got that right) on a discussion we were having about it and the trouble I was having sourcing meds. Tetracycline is all I can source here at a lfs, last time I didn't bother using it and tried triple sulpha.
"Tetracycline is most effective for gram positive bacteria, columnaris is gram negative. Nitrofurazone (Furan-2), Kanamycin (Kanaplex), or Minocycline (Maracyn-2) are better options. Triple sulfa can be hit or miss, works best if used early on.
Another note, gram positive antibiotics (like Tetracycline) are more likely to upset your beneficial bacteria than gram negative.
If tetracycline is all you can find then try it, if the fish don't show any sign of improvement after a few days then discontinue use. It is MOST effective against gram positive, but it may have an effect on gram negative.
I'd test your water daily while dosing any antibiotic just to be sure."