why do nice sold blue sps turn purple in my tank

[MikeEe]

Its not an ugly purple, but I would like to retain the nice blue colors that the frag had in other peoples tank.

For example, nice blue berman tort frag became blue tipped with a purple with greenish body

and now my bennett tort which was bright blue almost baby blue is turning more purplish everyday.

 

[Yinger]

I think a lot of it has to do with placement in the tank and lighting. I know with the blue hoeke, if you place it near the top, it turns into a lighter baby blue, but if you put it in the middle, it turns into a dark solid blue.