Blue cloves look washed out

[davidcalgary29]

Half of my rock of blue clove polyps look a little washed out and more grey blue than the lovely cobalt for which they're known. Is it a lighting issue? The washed-out polyps are perhaps 1cm higher in the water than the bluer half.

 

[fishface NJ]

have you tested your alk, calcium, nitrate and phosphate