LPS melting away

[ltjn11]

Help my lps corals are melting away very quickly Saturday night my torch coral melted away almost over night. Yesterday all looked good got home from work tonight my frogspawn has done the same thing. Water parameters are as follows Ammonia less then 0.1,nitrites show 0,nitrates 20, kh150,phosphates 0 or very close to it,calcium 440. I still have a bubble coral and an elegance that I don't want to lose. Any help greatly appreciated Larry