Oh, boy. That is a great question. The labeling is for mosquito control for water features and the dosage recommended for the control of mosquito larva is 2.5ml/1000 gallons. Which is an exceedingly small amount. So, I did have to guess a little bit here. But since this is a biological control, I used the hand-grenade approach with crossed fingers.
Here is what I did but don't take this necessarily as a recommendation:
What was treated:
Three canna "trees", four potted rosemary, about eight potted basil plants, two hot pepper plants, mixed containers of thyme, mixed containers of radishes, one cucumber plant. Probably around 50-60 gallons of soil/coco mix, overall.
Only the thyme was actively being attacked but as a preventative I also addressed other plants in the room.
I wasn't looking to drench the soil at first but instead just wanted to initially innoculate the media.
Took 1 ml using a syringe to 1000ml water. Applied the solution to all of the containers. Just dribbled it around the soil. Then did a normal watering but can't remember if and how long I had waited...
Gnats were knocked down within the period of several days. Thyme was heavily damaged but am thinking this was due to being attacked in the first place. The other plants have not shown any obvious signs of stress. Have not seen further gnats since the application.