Why am I having such a hard time with Tangs?

I cannot figure it out for the life of me, for some reason i just cannot keep a tang alive, i have a dual 55 set up with well over 200lbs of live rock and it is 100% biologically filtered, 440 watts vhos, use aragamite, feed with nori on a veggie clip as well as a special blend of food I make myself administered about every other day by hand, i supplement iodine and i use aragamight in my top-off water for supplements, there is a 15 gallon airstone in the sump, i acclimate using the drip method along with the airstone in the acclimation bucket. Anyone have any advice?

 

here are params as of 12/13
Calcium: 375
Ph: 8.1
Alk: 2.8
NH4: 0
NO2: .05
NO3: 0

 

Hi, more info is required. What other fish and/or other denizens of the deep are you housing?

 

The nitrites would scare me a little, there really shouldn't be any in a cycled tank. Did you recently add any rock or shells or anything like that?
Are you testing for the iodine? What else is in the tank? The other thing could be low oxygen, but you are running an airstone. In general, tangs require a lot more oxygen then other marine fish.
Do they seem to be dropping off for no reason, or do they get a disease? Are you running a grounding probe?

 

I have an false percula clown (i believe i got it from the person i bought the tank from), and a sixline wrasse. I also have a Green BTA and a plethera of corals

 

no grounding probe and i already stated the other inhabitants, i recently moved my rocks around and i think that might be where the nitrates are coming from, the airstone I am running is very small though, i had always heard that oxygen was bad for corals though, and they seem to just drop off or disappear

 

I have 6 tangs in my 155 oceanic half circle. 3 are over 5 years old, and i do way less then you mention. I do however have have a few wrasses, some cleaners. I see two of my wrasses cleaning my tangs nightly. I honestly believe the wrasse is the trick to keeping healthy tangs. Id start there.

 

As long as there isnt bubbles actually making contact with the corals an airstone is fine. Now did you mean nitrates or nitrites? Because you have in the OP as NO2, which is nitrites, not nitrates. Nitrites are toxic at any level, not like nitrates.
I would definitley get a grounding probe asap, regardless. But with tangs, they are susceptible to lateral line and hole-in-head, both of which can be caused by stray voltage amongst other things.

 

How many tangs have you gone through? Which ones were they and how long did you have them. And what did they die of?

 

I had an issue with the grounding probe at one time. I would make that first and formost. I have had had a few tangs in the beggining that did not make it. I now have 2 large yellow a large powder brown tang and a large blue hippo. They are my faviorite of all my fish and have had other tangs in the past. I would look at the nitrates to see if that might be the issue.