Ya, you can put some of your favorite fish in the 55. Go out and buy a divider, and divide the Severum and con from the africans (allow the africans to acclimate to the water). You won't able to add all of them, or you will have another ammonia spike (due to Bio-load).
What are your water parameters(125)? Your ammonia is probably off the charts. You can try some of that "Beneficial Bacteria" (BB) in a bottle; don't know how well it works. It's supposed to be a temporary fix until you get yours BB going (You have to wean off it of slowly to allow your BB to compensate.
If your BB is completely gone, put the fish you didn't put in your 55, into the 125. Check water parameters several times a day, and do a water change when ammonia goes above 1 ppm (IME don't let it go above 1 ppm or you'll start getting floaters).
Good luck and keep us updated!!!