People report success with a range of phosphate readings. Some people report issues if there's no measurable phosphate in the system, with a detection limit of about 0.03 ppm or so. If your tank is doing well enough, I'd leave well enough alone. We don't have enough data or accurate enough testing to be sure about what's happening with phosphate readings down in the 0-40 ppb range or so.
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Jonathan Bertoni
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