Joey's breeder said to look for white flakes, and it was a sign that I wasn't rinsing thoroughly enough. She said that most people skimp on this step. She also recommended using a good cream rinse/conditioner. You are not just conditioning the hair, you are conditioning the skin. She recommended the Biogroom products, and you can get a free sample by emailing the company.
Bio-Groom - Exceptional Pet Care Products for Over 30 Years The products are very concentrated, you have to dilute them. So far, no white flakes!
Remember, that just because something doesn't contain soap, it still contains "detergents" and these are different than soaps, but can be just as harsh on the skin. Rinsing is still very important.
Did your dogs have dry skin before the vet gave you the Epi-soothe? I like the Madan pin brush.