Yellow Tangs keep dying
I have a 180 gal
fish only aquarium that has been setup for about 5 months. Our fish include 2 chromis, 1 banggai cardinal, 1 stars and stripes puffer, 1 queen angelfish (juvenile), 1 powder blue tang, and 1 coral beauty. All added slowly over 5 mos. We have tried to add a (single) yellow tang but they both have died within 7 days of addition. My system was setup and maintained by a very knowlegble local fish guy. I do the weekly maintenance and he visits every two weeks (cleaning/ 20% partial water changes (last saturday before the second tang was added)). Both yellow tangs were hardy when obtained (eating, plump, and active) 2 different LFS
. My fish guy QT'd the second tang for 10 days and it was perfectly healthy when added. The there was some territory issues between the coral beauty and both yellow tangs. Neither Yellow seemed intimadated by the coral beauty though. Both tangs were perfectly normal eating/active the night before their death and the next morning each was found on the tank bottom gasping. One was placed in a hospital tank the second could not be retrieved. Both died within hours. No real signs of trauma (no frayed fins). Water parameters Sg
1.017, Ph 8.2, Akalinity 4.0, Nitrites 0, Nitrates 5 mg
/l, amonnia 0., T 80.7F.
Is the elevated Nitrate level the result of the dead Tang? I plan on a 20% partial water change tommorow. My fish guy thinks the Coral Beauty is the source of the problem and the Tangs are dying from physical trauma/stress. When a fish dies from a failed acclimation would it normally get sick, waste then die slowly versus as in this case perfectly normal then sudden death? We plan on removing the coral beauty before adding another yellow tang.
Any help would be appreciated. Thx.