I do vodka dosing in one of my tanks without any problems. There is a very easy to follow chart available online. Also, have you tried Purigen? I keep a bag in all of my tanks. It helps with nitrates and nitrites.
So I took a water sample to jays today. The nitrate test came back 0 and phosphate was 1ppm. Told him just bought a new nitrate test the other day and mine read 80ppm+. He told me to bring them back and will replace them even though they don't expire til 2019..
Well I guess that's good news. Too bad you spent so much time and effort only to find out your tank was fine. I'm glad that it all worked out. Chasing numbers always leads me to more problems. I end up fixing one at the expense of another. Nice that he's letting you return the defective kit(s).
Stirring up the sand bed releases nitrates from the sand. I never touch my sand bed I use nasaris snails hermits and turbo snails they take care of it.