New to WFP and for the life of me I keep getting spots on the glass and runs sometimes. My TDS reading is 0 or max 2. I use a backpack with a 70psi pump with a variable setting or a on/off switch that runs the pump at max and it does go through some water so i use the variable setting to try and save on water. Am I just not using enough pure. Just want to ask how much water should I be using on say a 8 window semi. Done a few paid jobs and went back to check and was shocked how **** the windows looked, so did them again but trad. Struggling with WFP at the mo to be honest and confidence in using it is real low.