i have seen a few topics on folk claiming doubling up there di vessels, and claiming to get 3 times longer, some how i can not see that happening, for instance if you have for argument sake, 50ppm 1 vessel you get 4 months, so if you double up you should just get around 8 months, i just can not see how it can give you 12months, or longer, i think it just saves on changing resin, or no one has really done an accurate record of water they have used, or less work than normal, i could be wrong, what do you guys think