Steve,
From what I understand, Triggerfish do not thrive in a 125gal tank. Sure, they seem to "fit" just fine, but they do not adjust to being confined. The result is very sad, as the fish will pace back and forth. They continue to eat and live, but they are visually unhappy. If there are any Triggerfish that are an exception to this rule, then someone will have to correct me.
People often get hung up on volume, but from my experience, the length of the tank is the most important dimension, followed by height, followed by width. As far as a fish is concerned, I have observed very little difference in behavior in an 18" wide tank versus a 24" tank of equal length. I am not sure a 180gal would solve the problem of keeping a full-grown trigger, but again,s omeone would have to correct me.
However, bigger is better, if you are prepared for:
- The added weight
- The added expense
- The added maintenance
A 180gal does afford you more fish, and it gives the fish more room, which is always good.
My idea is to sit and think about what you are prepared to handle and maintain, and what you really want in your tank before making your decision. People always advocate a bigger tank, and they have a point, but my well-maintained 125gal system is better for fish quality of life than someone's poorly maintained 180gal system that they purchased but can't take care of.
Buying fish is the most fun part of the hobby, but it is also the part of the hobby that should be done with the greatest degree of caution and as slowly as possible.
I keep a Powder Blue in my 125gal system. I know many other reefers locally (and others who have been featured in Reefkeeping magazine) who do the same. From all of our experience, the general consensus is that a 125gal system is acceptable, as long as there aren't any open water column swimmers of similar (or greater) size and behavior.
A Powder Blue Tang is a very challenging fish to keep.
Over the years, you can learn to keep one, but they are very difficult. I would not attempt one without a:
- quarantine system
- established display tank
[/list=1]So in short, this is a fish that I would add to your 125 or 180gal system after a year or two when you have a full setup up and running.
PBTs also vary in personality like most fish. Hoewver, they can be on the aggressive end of the tang spectrum, and thus, it is almost an absolute necessary to pick one out in person who is alert and inquisitive but not skittish, overly hostile to tank mates, etc.
I hope this advice helps.
Matt