Interesting, I actually RECEIVE my gnats from that soil, albeit the perforated bags probably allow the bugs in the local grow shop to move in. Be aware of bugs when you buy. One shop here stores soil outside in a barn but the other has it inside all nice and climate controlled.
Look into "bud washing" by DocBud. Prominent online artist that is easy to find. Uses a 3 step rinse, warm hydrogen peroxide, cold lemon juice, cold water. It's kinda nuts when you try to wrap your mind around it but it gets rave reviews when people actually do it. Gets rid of everything nasty you don't want to smoke like dust, hair, mold and powdery.
Haven't tried it yet but I should have enough to give it an honest trial in a few weeks.