Now for an opposing position...
I have two tangs.....a Blue Hippo and a Yellow Tang in a 4' tank. However, it IS a 120 gallon. This means that they have two foot back and four foot long. I know that longer is always better than depth, but depth DOES make a difference. (As the owner of two oscars in a 120g, they do well. Putting them in a 75g would not work. It would be cruel.) They have been with me three years now and get along great with each other. Both are at about six inches to eight inches. Currently, there is also a Silver Scat with them. He is the same size. I got him to clear out the aipstasia (sp?), and he did. I know that he will need to be moved. I plan to set up a 75g SW FOWLR
. He will probably end up there. There are a couple of smaller fish (clowns, goby, gramma) with them. As of now, there are no corals.
I confess that a few months ago, I tried to add a Kole Tang, but it died in a week or two. My guess is that one of the two tangs badgered it to death. I made the mistake of adding one more when I knew better.
My two tangs were put together when they were both small within a couple of months of each other.
The Yellow tang is not as much of a fast swimmer as the Blue Hippo. The Yellow Tang spends his (or her) day picking at the live rock, and the Hippo spends most of his day swimming around. He does some picking but he tends to enjoy eating the food I give them more.
I change 40% of the water every couple of weeks. The nitrites and ammonia remain always at zero. The nitrates usually stay below 20 or 30 at the worst and are better, too.
My only error was about a year ago before I QTed fish. At that time I lost most of my fish to either velvet (most likely) or ich because of a fish I had added. Normally all of my fish came from one lfs
, but this time I went to a different store. My mistake. The point is that of all of the fish, only the two tangs, the scat (which was most likely the culprit for the disease) and a goby survived. (For 2 1/2 years, I never had a problem with not QTing, but as happens to everyone, sooner or later we get bitten.)
The tangs, even though to the point of death (the Blue Hippo was actually blind from fungus) before I tore the whole tank apart, QTed them and redid the tank, came out fine. They are hardy fish and still are doing very well. There are rare disputes of any kind and they swim as if "buddies."
I can say that I would not put two tangs in less than what I have, but even though it is a four by two, they do not appear to have any issues.
One thing I can say about most fish after getting a bigger tank....a bigger tank is always better. Even if I had a group of neon tetra or a group of chromis, I can say that it is much more enjoyable to watch them swim in the biggest tank possible. So it is with bigger fish. Bigger is always better, but IMO
my 120g is sufficient and fine for two tangs.
One would work in a 75g, but not two. One Yellow in a 55g would work, but not one Blue Hippo.
BTW, if you have room for a four foot tank and not for a six, then now before getting started too far, get the biggest four foot tank you can get. If you have room for a six foot tank, then don't just get a 125g...get the biggest six foot tank you can.
Just my opinions.