My 2 cents: gnatnix isn't a viable option in my experience. Try beneficial predators.
Chunky stool is on point.
Gnatnix is dusty. I use fans below the canopy, and became very concerned about the fans blowing dust up and onto flowers. In the end, I couldn't take the risk.
Are you doing hydro or soil? A convention often repeated is, if you have gnats, let the soil dry out significantly, then let the soil dry out in between watering. Drying out the top of the soil creates an inhospitable environment for the fungus gnat larva, disrupting the life cycle of the fungus gnat.
But there's a delicate balance. I often couldn't dry the soil out enough to completely eradicate the fungus gnat larva, thus the adults. Also, drying the soil out so much seemed to impact my growth. It's not that I noticed significantly less growth between traditional water from top or bottom methods and letting the pot dry out enough to kill the gnats. It's that once I started using a SIPS pot, which creates a constant level of soil moisture and avoids the drying cycle, my growth exploded.
You're already where you are. Many people speak highly of gnatnix. After throwing away the entire half of a canopy due to concerns about gnatnix drifting up and settling on flowers, I decided to figure something else out.
I use predator mites like rove beetles and hypoapsis miles/mites. I have used nematods; it's possible they are still there, but I can't tell.
I've had the same crop of rove beetles for nearly a year and a half. I chopped, put the smart pots in trash bags for a few months, opened the bags and saw that the rove beetles survived. Every time I transplant something into another pot, I put a few rove beetles into the new mix.
Grab some sticky traps; put fans below your canopy, blowing on top of the soil; use and repopulate new pots with predators.
I'd hope you can salvage this one, and that in the future you can keep populations down.
I wish more people would look at this issue with me:
for anyone that has every moved their hand through a bag of gnatnix or tried to put that stuff in pots that already have flowers, how does one keep that powdered glass from blowing up into the flowers?
The only option is to have no air movement below the canopy to prevent the gnatnix from being disturbed and, potentially, ruining the flower.
I'd rather have fans above and below the canopy, beneficial predators, and sticky traps.
Good luck.
