Hi! If its brand new carbon, do a big wc, run it for a couple of hours and do another wc. You should be good to go! Lynda's suggestion of culling the sick fish may be something you have to seriously consider in the future. You have tried a slew meds with zero improvement and/or things becoming worse. After the tetracycline, there really only is the expensive stuff left to try. I am really hoping the combo of tetra & dips helps but I suspect your fish have quite a degree of antibiotic resistance. This is not your fault & your doing your best to help your little guys!! For now, all you can do is keep trying & hope for the best!