Furan or sulfathiazole. Tetracycline has not been as effective In my experience.
I would always plan on dosing not only and antibiotic, but also a good quality anti-parasitic (Praziquental). When we get wild polys in they very often have an external parasite called macrogyrodactylus worms. And these worms almost always lead to septicemia as a secondary infection.
Make sure to carefully check for these external worms as they can lay dormant for months and suddenly become extremely aggressive.
This is a CB bichir and it was moved from its display tank at the LFS, to my parents house overnight, to my apartment. I couldn't go straight to my apartment 45 minutes away because I work 5-11 on saturdays and the LFS was closed on sunday.
He is recovering. The redness in his finlets has all but vanished. His pectoral fins are losing their color as well. He is quarantined in a 20 long with two sponge filters. I dosed Furan-2 and salt. I can't wait to show pictures. He's a one of a kind beast. Unfortunately his external gills have receded since I have owned him.
Thank you for everyone's help. I just wasn't sure which medication I should have used because there are so many that claim to treat septicemia. I couldn't afford to dose the wrong one.