I would say people shoot for around .02-.06
However I'm not an expert. But I think people have success with higher phosphates. high phosphates and nitrates can cause algae.
my nitrate is 50. and my phosphate is 0,5. my gonıoporas are happy. my chalices and favıas are growıng. colors are brıllıant.so ıt ıs all about the adaptation of living things to the environment