Sorry re-reading this post and see I missed this.
I'm weird, I think most people feel I go way overboard, but I try very hard to keep conditions clean and as sterile as possible in the grow space. I'm unusual because I also do other stuff in this space like grow mushrooms and do tissue culture, both of which require sterility for at least part of the process. But if I got a case of PM or Bud Rot or Pythium, I take that very seriously as it impacts what I am doing outside of cannabis.
With strict cleaning I have not had a pest in years, knock on wood.
Some of the stuff I do to not introduce the baddies, or stop them quick if they get in anyhow:
Ethanol based hand sanitizer (also works really well to get the sticky off your hands / gloves)
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Drains are the biggest problems for gnats. They are most likely where your infestation would start.