Microbe Lift BMC
10 drops to 5 gallons of water and you have complete annihilation of any gnats while staying 100% organic and harm free.. That stuff will annihilate most soft bodied insects just like Spinosad.
Bacillus Thuringiensis Israelensis (BTI) is allowed to use even in California grows. It will drop them gnats, mosquitos and soft bodied flying insects like it's hot.
Fun Fact Spinosad is not allowed in Michigan for cannabis cultivation even though there are OMRI versions and it's considered to be safe. ¯\_(ツ)_/¯