I have good luck with Wolman's powder wood cleaner. It is a pain to use sometimes because of the mixing but for the environment and its cleaning ability I am satisfied.
We use granular oxalic acid for brightening and mill glaze removal. Mix about 1/2 lb to 5 gallons of water and apply...dwell for 15 minutes or so depending on the temp and such then rinse well. It's also much more affordable than commercial products although you do have to take more precautions while using it (toxic). Oxalic will only dissolve into a 10% solution at most so you can adjust your concentration up to that point, otherwise you'll have alot of sediment at the bottom.