Corals turning almost white

[CandyCane]

I have 6- 18watt T5 bulbs about 4 inches above my tank.

Some of my corals love the light and others have been turning white. My kenya tree corals- 3 of them- are all very white and my frogspawn is also loosing its colours along with my zenia. My pulsing blue zenia however is at the top of the tank and has kept its colour just fine.

So besides that their "bleaching" they are full and all out and show no other signs of any problems

Any idea's of why the algea inside them is dieing? At least thats what I think is happening