I always use a tissue to grab the vial. Finger prints are enough to throw the whole reading away. Alongside, one tiny floating particle in the vial is also enough to give you false reading. And the worst part is the 3 min shut down time. I don't know what the people at hanna was thinking? I guess according to them, its "cost effective" to throw away a dissolved solution than to change a battery for adding an extra minute to the shut off time, not to mention the dedication to pour the powder in and the two minutes shaking time. I really hate this photometer from the bottom of my heart but well, if I get everything 100% right, I know I am going to get a much more reliable reading than any other test kits. But reaching the 100% takes a lot of work and luck too.
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You wouldn't want to see my tank. I don't use fancy equipment and I am a noob 
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