Mallet 75 WSP Systemic Insecticide is specifically designed for mix rates per packet. There is no real way to accurately dilute that down. Dominion 2L may be a better choice for you. Dilute at .2oz per inch of trunk diameter.
For adelgid control, Mallet 75 WSP Systemic Insecticide is mixed at 1 packet in 300 gallons of water as a foliar spray. It cannot be mixed in any smaller quantities than that. It should be applied as a foliar spray or as a soil drench. It is not labeled for a basal trunk spray. For a soil drench, you’ll mix 1 packet per 12-48 inches of trunk diameter at breast height in no less than 10 gallons of water per 1000 square feet as a drench around the base of the tree. You can use a surfactant like Hi Yield Spreader Sticker if you’re using the Mallet 75 as a foliar spray. There is no specific pH listed on the product label, but generally the pH of your water is recommended to be between 6-8.