This reference guide shows the various concentrate mixing ratio and dosage units for the Pro Line. Athena recommends mixing concentrates at 2 pounds per gallon. If you mix at a different rate, be sure to adjust your batch reservoir mixing rates to hit the desired EC.
Metric recommendations are based on 2 lbs per 4 Liters. Note that this is a different dilution that Imperial and use the correct dosage reference based on the stock concentrate you mix.
Download Dosage Reference Guide