Depending on the model of Hanna Checker you have, read the instruction manual. Some of them you are supposed to divide your digital output by 3 to get your actual reading. If this is the case with yours, your phosphates are truly only .05 which actually is pretty good.
I find that if your phosphates are too low, corals pale a bit, anything over .05 to .07 and you start to see algae show up.
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