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From what I have read on other postings they say the acceptable is 0.05 if you have corals. I have a reading of 0.10 and my soft corals are doing great.
It depends on the type of coral you keep. Phosphates can lead to algae which can overtake a corals skeleton. They also hamper the forming of the coral skeleton in hard corals, mostly concerned with sps corals in this regard. High phosphates also lead to colors to brown out.
Your soft corals don't care about your phosphates because they don't have a hard calcium skeleton like Lps and sps.
Fish tollerate it better, but high phosphates are what I look out for the most. Soft coral .1ppm is okay, but for SPS it needs to be .05 ppm or lower. I use Hanna as I get consistent readings at these lower levels.