Is there no hint of purple even when the drops first go in?
Are you following instructions properly or the nitrate test? shaking bottle 2 for 30 secs then test tube for 1 min? if not nitrate reading wont be accurate.
Andy
Nope, no hint of purple at all, just turns bright pale blue.
Yep, doing that exact same routine. Feel like a bit of a berk standing in my lounge window, shaking my fist at any passers by whilst counting in my head . In fact, I normally read the instruction booklet before each test just to be doubly sure I'm not getting it wrong.