So corals brown out over .4 , that’s going to get debunked quickly I’d sayI don't have exact numbers, but when i see corals starting to brown a bit, I mix 7ml of seaklear phosphate remover into 1 gallon of rodi and constant dose it until it's empty. The gallon mixture lasts roughly a week.
I haven't tested in a while, but I'd imagine ime well over 0.40 ppm