Freshwater dips are usually just 5 minutes so I never worry about the PH. If your worried about it, you can splash a little tank water into the dip container to help buffer it some. Doing a freshwater dip is super easy. You'll want a container large enough to fit the fish of course, then an air stone and pump. You'll want to temp match the water they are coming from and run the air stone the whole time they are in there, set your phone to count down 5 minutes and put them in! Keep an eye out to make sure they dont try to jump out or anything as well. Why are you thinking of dipping the tang? Do you suspect flukes, brook or velvet?