My powder black tang today suddenly died in New to the Marine Aquaria Hobby Posted July 30, 2020 Thanks to all of you who replied. My grateful thanks to all. My other fishes? I hv 1 foxface rabbitfish, 5 damsels & 1 baby blue tang. No corals. How are they doing? They seem ok except for blue tang. It doesnt seem to want to come out of the rock. It keeps hiding there. I did a PH/ KH test. If I did do everything correctly, the reading is 6.5. Nitrates are 50. So its rather high. I hv overfed the fish I think. But am now cutting back on that. Finally, I hv added the required dosage of Paraguard into the tank. 5 ml per 40L . Do I still need to quarantine the fish? Is the water contaminated? If all the fish within are sick already and slowly suffocating with velvet what should I do? Help!