hey marc I too open both ends on the 2 products you can do that too but you will see when you start dosing that the glass stays the same color as the product inside. this means you are leaving product inside. I do take a cup of water from the tank for each seperate vial and mix each seperately. but when you hold the vial in front of a powerhead/tunze stream in my case and spin it to get it from all angles the vial will turn a transparent yellow and then you will see how much you would be missing if you didn't do this. the selco concentrate not the so called selcon concentrate is very thick and sticky and I would guess you might get 25% more product doing this. just a thought I am sure someone else will chime in after doing this themselves. when are you supposed to start your dosing?