I'm concerned about cleaning my fermenter with PBW. The crystals seem hard & sharp and take a while to dissolve. I don't want to scratch the bucket. Am I doing it wrong?
As long as you do not begin abrasive scrubbing until the PBW crystals are dissolved, PBW should not be a problem.
Let me differentiate between HDPE plastic bucket fermenters and PET carboys (like Better Bottle).
I find that I don't need anything other than hot tap water, a soft sponge, and a slight amount of elbow grease to clean HDPE bucket fermenters. Exposure to PBW for a short time shouldn't hurt.
But it is not recommended to use PBW or Oxy-based cleaners for PET carboys because it causes stress corrosion, and eventually will lead to clouding or failure of the PET carboy.
Better Bottle recommends using Free & Clear Natural 2X Seventh Generation detergent, an enzyme based cleaner in this study of the effects of various cleansers. What works for me is adding a small amount of hot tap water, a small amount of cleanser, and a washcloth, and rolling the carboy on the counter or floor. The washcloth rubs off all of the krausen rings.
Edit: it is not recommended to use PBW or Oxy on PET.