Maybe, maybe not. I'd like to know how big this Achilles is for $170?? :eek1: That's a steep price I think. At least you'd be adding the more aggressive fish last, and the tank is somewhat large...but it still might not work out. Depends on the temperment of all 3. They are like people, no 2 are the same.
If the yellow is larger and well situated to 'his' tank, he might be aggressive towards a small Achilles. If the Achilles is large, then he might go in like Rocky Balboa...lol. None of these things are a gurantee, you will do it at your own risk. How much live rock you have, more importantly how you have your rock PLACED (caves and such) is another factor. You might want to reaquascape just before adding an Achilles. Since the Achilles 'should be' more agressive than a yellow and hippo you should add one smaller than the 2 established tangs. Just be ready to remove one if it doesn't work out.
Also, make sure the Achilles you purchase is HEALTHY. I'd watch him at the LFS for days/weeks. Then quarantine it when you get home FOR SURE. Keep a good eye on it for disease and how it eats. MAKE SURE THE TANK HAS GOOD WATER MOVEMENT. I personally think that is one of the most underrated thing people think about when considering an Achilles tang. The water must be full of oxygen and have STRONG flow throughout. A friend of mine had an Achilles in a 180 for years, it was the healthiest tang I've ever seen - fat as anything - but the flow in his tank was insane.
Lastly I'd like to say that just because you have the size situation figured out for the beginning to work out, when they get older all bets are off. You might add a juvenile Achilles that turns into a butthead in years to come. Same goes for the yellow though...I've never had aggression issues with a hippo. That's not to say it CAN'T happen though.
Hope this helps.
P.S. Did I mention the water movement in your tank should be substantial??
