Miller,
What is the relative size of the Regal Tang compared with both Yellow Tangs? Nobody thinks that Tangs are capable of ichthy homicide, and yet one of our local club members had a Sailfin tang go beserk overnight and kill half the stock in the tank in one fall swoop. This was in a well established 300 gallon tank, so even tank size was not as big a concern as one might initially guess.
As already mentioned, if you are going to stock heavy (and can't upgrade), you would be wise to drain the tank (store livestock in plastic tubs/garbage cans temporarily), drill an overflow if it doesn't already have one (see glass holes.com for one idea), put a cheap plastic tub or stock small aquarium in as a sump and get some circulation of any sort going initially in there. I would go with a Mag 18 or equivalent if you can afford it for that size tank. Otherwise in the meantime adding an additional powerhead in the tank and arranging all powerheads in the same direction lengthwise at the same end of the tank to create a gyre can improve your circulation (versus having multiple directions partially cancel each other out).
