Little B...tards. I thought the adults were just flying gonads. Maybe they laid eggs in there. I do not like fungus gnats.
I used about $20 worth of BTi on my indoor soil grow, to no bloody avail. The little buggers managed to escape and do serious damage anyway. I caught about a dozen of the larvae chowing down on the roots of one of my youngsters. The buggers managed to convene for a collective meal in only a day or two after I planted the tap rooted seed. There was no hint of them in the hole I dug for the seed. They heard the dinner bell from wherever they were lurking, and high tailed it straight to the table. I might have been able to get something out of the mess eventually, but given how bad the damage was, I walked rather than investing more time.
I'd like to do a water only grow, but it will have to be without gnats. I may sterilize the soil I kept from the trashed grow and innoculate it with bennies after. Or just make some super soil from scratch indoors. The thinking cap is on.
I am also thinking about a grow with Bugbee's peat vermiculite mix and MC 2 part. I would have to do some figuring on the dolomite and gypsum addition because I think his proportions may have been tailored to his tap water, and my melted snow will be far softer, pretty close to RO. And, MC is different than his nutes (maybe Jack's, but an odd 20-10-20 NPK ratio that I can't find).
No shortage of options, and all of them likely to be another learning experience.
Good luck killing the last gnat.
ps. I cracked and ordered a par meter. Not an apogee given the price, but not bad reviews, so we shall see. If it works as advertised, we will find out what those screw ins are up to.