My personal preferance for the numbers:
ph 8.2-8.4
kh 15-17
Going too high on the kh can cause them to lose color as well... and not breed as often. So try to stay below 20 or so IMO.
If you don't already know this... BS cannot bring your ph any higher than 8.2 but it can sky rocket your kh .... so basicially keep an eye on your kh before you get your routine down. Once you've got everything figured out... all you need to do is test your kh once in a while. No need to test ph unless something is wrong
As Charlie stated I don't mess with my gh. I used to... and figured out that it is really not neccessary. All it did was cost me money and stress the fish out when I messed things up with the salt.
I don't want the ph meter for tangs lol... it's the plecos