Yes. It's a product of evaporation, and the level of dissolved solids from the combination of fertilizer and the level of dissolved solids in your water. It's not unique to Turface, however - it occurs in all container soils. If you don't like the appearance, you can help reduce it by wetting the top of the soil with a little water & coming back a few minutes later to finish your watering. This is the most effective way to water a container anyway.

Al