Whether to use GFO for phosphate of 0.03 ppm in SPS tank

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I have mostly SPS, growth is good but colours are not as nice as I'd like in some of the corals, for example one coral that arrived dark purple to bluish is a light pastel shade of purple.

I use a skimmer + adding sugar + have a refugium with macroalgae. There is no algae growing in the display tank.

Water parameters are in line, zero detectable nitrate by Salifert test, Alk is targetted at 10 by Salifert test and Calcium around 400. Phosphate by the Hannah phosphate checker is 0.03 parts per million.

So I'm wondering whether lowering the phosphate level to zero would help the colours in my corals, or is 0.03 ppm a low enough target.