ok so 22 cf is same as 2.,2 ec. there are 2 scales to convert ec to ppm. multiply the 2.2 by .5 or .7 conversion factors and thats what the ppm will be, use the .5 scale. so at 1 ec its 500 ppm. 2 ec is 1000ppm. shouldnt even need more than about 1200 to 1500 ppm at full feed.