FYI, if you use mosquito bits in your grow to combat gnats, you can buy the stuff as a liquid and way more concentrated.
Amazon product
This will treat "400 gallons every other week for 2 years" So 400 x 52, so 20k gallons of water.
It looks like its a powder, but when you open that container, its actually a dropper bottle. I've just added a drop of it to each of my reservoirs. This summer I'm going to spray my yard with it, I get so sick of being attacked by mosquitos.