A couple of things I have noticed about PBW. It works much better with soft water at low concentrations, like 1/2 -3/4 oz per gallon. It actually is not as effective at too high a concentration in soft water. I do use acid then PBW on the Kettle and Mash tun. And if I have a really filthy unitank that has had beer in it for a long time. So if you have soft water use less PBW and check the results. Also if you are cleaning bright tanks that have held filtered beer you should be able to use Acid #6 or an equivelant as a stand alone cleaner with no caustic/PBW. You can also clean under pressure if only using acid and this saves time and CO2. I will clean under pressure once then open the tank on the next round to visually check and i have had no problems when doing this. Occasionally I will use PBW just to be safe. Birko printed some articles about the logic behind acid then caustic. Rather than try to remember what was said I would refer you to Dana at Birko I'm sure he would answer your questions and forward this article.
"You are what you is." FZ