Azamax as a root drench does not affect potency, flavor, smell, or benneficials. The best measure is to stop overwatering and you wont get fungus gnats. Also never buy soil that is stored outside. Any reputable and knowledgable retailer will know to store soil mixes out of the weather. If you still get fungus gnats and your growing in soil use benneficial nematodes such as Scanmask. They are kinda expensive but they will kill any pest in the soil without harming anything including bennies and flavor and smell. They are a natural preditory nematode and only kill pest species. They colonize the soil and last the entire grow. You can also reuse the soil for several grows and the nematodes will remain as long as you dont allow the soil to completely dry out. If it does the nematodes will die because they need moisture to live and travel. Also a great antipest for outdoors too. They kill hundreds of soil born pest like June Bugs, Pill Bugs, ect.. And even termites!