I had absolutely no gnat problem with the outdoor run EB. Now that could have been from the higher temps.
I'm fairly sure they came from my ewc and they were kept in check by the good bugs. If the ewc wasn't the source, the one change I did to under the cover gave them a good environment to thrive in.
I wasn't happy with the active mycelium growth when applying bokashi to the added compost at top dressings. The compost mites would just eat it up. To solve this, I added two empty small cans to raise up the cover and give the mycelium room to grow and get better established. It performed as expected and the growth was
very good for a well established mat.
I'm now pretty sure that gave the gnats an optimal living and breeding environment......no matter where they came from.
I did knock them down with the application of the DE, but not out. I also just had to slow top water the other potted girls to get a better full watering. So today I'll take care of a little snipping here and there on the girls to neaten then up. Then it's just gonna snow on all the girls in the tent with a heavy dose of DE. I'm good with no more top dressings on any of the girls with the time left and the nutes I have banked. I won't really have to worry it crusting up.
The EB girl has drank her two gallons in three days, so I'll be good to carefully do a drench with Dr. Zymes before the DE application. Yeah, that will blow all my good bugs, but it won't matter much at this late stage.....probally two weeks.
In future EB grows, I guess I'll just use the cover with no cans creating a big area under the cover for them to safely thrive.
I don't know if having a living cover crop, sans cover, will help with the gnat problem or not. One could include some plants that repel them and NOT something gnats seem to be attracted by.
Another option could be to use some fermented garlic and/or plants that gnats don't like as a preventive.
Edit.......Yeah, I know that the mycelium is sort of like icebergs the vast majority of it is below the surface and I should be happy with any surface growth. Just a bit too much of that more is better attitude.