Sudden anemone colour loss

[Rapide]

In the past few weeks almost all of my carpet anemones have lost some of their colour. The only one that hasn't is my oldest one, the white striped green haddoni. The blue haddoni has had some colour loss, and the bright, almost neon green "mint" haddoni has turned into light green - almost bleached looking. Yesterday it attached it's foot on a rock and out of the sand.
The S. tapetums haven't actually lost their colour, but turned brighter, almost fluorescent. Also a mystery anemone that I got from another tank has slowly turned bright white. It used to be light lavender with purplish tips.
Quadricolors and Phymanthus are doing great!

There has not been any radical changes. The lighting is the same, and everything is in order. The only thing that has changed lately is the PO4 and NO3 levels. The NO3 used to be really high, over 100mg/l and has slowly dropped to ~20mg/l during the last 3-4 months. The PO4 seems to be under detectable levels, but I'd say that it's something like 0,05mg/l because I have large fish and feed a lot so there must be some.
Alk. 8°dKH, pH 8,22 - 8,31, calcium has always been high, NH3 & NH4 are 0. Magnesium has been a bit low always because of the high Ca. That will change soon.

Could the reason be my ATS? Maybe the algae sucks all the amino acids?
I use the Balling method for dosing (CaCl2, NaHCO3 and NaCl free salt) + iodine, Tropic Marin A&K elements (20ml/day).

All in all everything is fine... One change is that I added more water flow, but this wasn't untill recently.
I'll do a 118 gallon water change today and see if it does anything...

 

[PGLoynd]

Since the color change was gradual, I would consider lighting. Possibly too much or not enough. I have found that I have to move them around the tank, leaving them in their new spot for a few weeks (unless they move on their own, as my RTBA did when she was unhappy). If they continue to lose color move again. It really can be hit and miss if all water prams are good.

 

[Rapide]

It's impossible to move them... I can't even reach them.
I don't think that it's because of the lighting. Some are under fluorescent bulbs (8 x 39w) and others are under LEDs. I have a new 600w LED on the way, hence the T5's.
Stichodactyla tapetums are close to the surface, and haddonis are on the bottom, so they get a different amount of light but the symptoms are the same :/
The green whitestriped haddoni is not in a direct light, but it's doing fine. The blue one is just under a 144w LED, and it's OK. It hosts a pair of ocellaris. I shot this a couple of days ago, http://http://www.youtube.com/watch?v=ZfIfTtJbbw0