help: bleaching at the base

[bourbeaue]

I have two SPS Corals that are starting to bleach at the base. One is a frag that has been growing well for about 3 months now. As of lately, the first half inch above the blob of epoxy holding in place has turned from pink to white. I am not sure if there is still ttissue there. Probably as I can still see polyps in the bleached portion. Another one has a fairly large section between it rock base and the main body of th coral that has no more tissue. Is this an indication of something missing in the water ? My Alk, Calcium, ORP, temp, nitrate and phosphate are fine.

Thanks for your help.

E