[South Bend Bob]

I desperately need help with Yellow Tangs! I have a mini-reef tank set up as outlined below but can not seem to be able to keep yellow tangs. I am on my third yellow tang in one and a half years. I have not had on live beyond 3 weeks, and this newest one had Ich show up in less than 24 hours!
I know I failed the #1 rule - Quarantine! - but I have had wonderfull success with other fish from my dealer and fully trust my dealer. This Tang was in his tank for about a week and was fine until I put it in my tank which I believed to be established.
I have had the tank set up for a good year and a half now and the current environment has been as is for nearly a year.
What is the secret to success with Yellow Tangs?
*Here is my tank;
75 gallon (48x18x20h).
1.5" fine aggregate/crushed coral & shell substrate.
50+ lbs live rock - lots of coraline (sp?) algea, some hair algea
and some polyps & small feather dusters.
1 CPR BakPak 2R Skimmer.
1 Wisper mecahnical filter.
2 175w PFO metal halide lights 12" above the water level.
1 powerhead mounted on end glass 4" above substrate.
1 VisiTherm heater
*Water paramiters;
PH - 8.3
Calcium 450
SG 1.023
Temp 81 deg.
Amonia, nitrate, nitrite & copper not measurable (too low).
10% water change monthly - last done 10/11/03.
*Livestcok;
3 Yellow tail Blue Damsels - 11 months old.
2 Tomato Clowns - 10 months old - spawned in July - no luck
raising the fry.
1 Lawnmower Blenny - 1 month old.
15 Blue Legged Hermits - 14 months old.
2 Black Mexican Snails - 18+ months old - my only originals!
1 Emerald Crab - 1 Day in tank.
1 Yellow Tang - 1 day in tank.

I had a 7" long Yellow Tailed Corris Wrasse about 8 months old,
but he killed & ate 2 Emerald Crabs & all my Pepermint Shrimp so
I traded him back to my dealer and gave another shot at the Yellow Tang.
I feel like I'm starting all over again. I went though the following fish, never ablbe to keep more than 1 month, before my tank matured to where I could keep any fish;
-several Damsels (Blue, 3 Spot, Black & White)
-2 Yellow Tangs - last on before this was Oct. of 2002!
-1 Powder Blue Tang (too eager & cockey to wait!)
-1 Long Nose Butteryfly
Any help will be greatly appretiated! Also, should I quarantine the Tang now or is it too late - The rest of the population is doing great.
Thanks, Bob.
-

15 aprox. Blue legged hermits.