Trick to clove polyps?

Can someone tell me whats going on? My clove polyps seem to be thinning or dying! They are a few inches off the sandbed in medium flow.

LED light

Mag: 1350

Alk: 8 dkh

Calcium: 450

Ammonia: 0

Nitite: 0

Nitrate: 20

Phosphate: 0.03