Let's take a vote. Which one? I got the Low as a Christmas gift. Do I need to return it for ultra low?
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I think you might be confused between the two. There is a Phosphate low range and then there is a Phosphorus ultra low range checker. To be honest, most will not need the Ultra Low Phosphorus checker. I have both but since my system suffers from ultra low nutrients, I need the phosphorus checker.

