My display tank is currently fallow, as I am treating all the fish for ich/flukes. I have finished the QT of my fish and cycled a temporary 30 gallon tank and transferred all my fish to the tank until the DT fallow period is over. I have seachem badge on the cycled tank and tested the water when I transferred my fish to it. However, I have been keeping any eye on ammonia using seachem badge. I assumed everything was fine, until I noticed my yellow tang started getting a red coloration on her mouth and stopped eating. I changed 70% of the water as a weekly routine and continued noticing that the yellow tang was not eating. Therefore, I checked my parameters and found 0 ammonia, but 0.25 PPM of Nitrite. If it was 0.25 PPM after 70% water change, the Nitrite level must have been pretty high before I did the water change. Long story short, the same day one of my chromis died and I added some bioballs from a clean tank, added fritz bacteria and monitored the Nitrite levels. I also added prime to make the nitrite less toxic. Next day I did another 70% water change and cut down on my heavy feeding, the nitrite level has been at 0 since then. However, the yellow tang has not started eating yet. It still has the red coloration on its mouth and breathing heavily. I just moved it a separate 10 gallon tank, so that I can feed it without competition and probably treat it with medicine. It is still not eating. I have the following medications at my disposal metroplex, kanaplex, maracyn 2 at my disposal (anti-bacterial). I have posted a short video of the yellow tang. Rest of all the other fish seem to be healthy and eating well. I dont want it to die, please let me know what I can do at this point of time. @Jay Hemdal - Any advice would be greatly appreciated.