Corals missing colours & rtn ?

[Aquopolis]

whats happen in my tank ?

In a week ( + or - ) some of my SPS's are diying slowly, missing colours
and rtn. I'm doing now serious water changes,triying stop this. My parameters are corrects....
Ph 7.95 to 8.41 ( depending of the light )
kh 7
ca 430
Nitrate < 10 ppm
phosphates beetwing 0 & 0.1 ( azoo test suck )
salinity 1024
temp about 26 ºC

here u r , some images....

Acropora Sp.

Acropora Sp.

Seriatopora

Acropora Sp.

Stylophora

Please, help me.

Cheers
Manuel Barea ( spain )
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P.D. I just test my Mg levels, and it overdose.. probably mi salifert test dont work fine,because y dont add Mg until 3 weeks ago... its saids about 2010 ppm of mg... if we supousse that the test are right, can be it my problem ? i dont found anything about toxicity of Mg in aquariums, or the effects of overdosing mg in reef aquarium... any idea ?

 

[Maoiwowie]

How old are these specimens? How old is your tank? And by now im sure they have perished. What kind of lights do you use? As far as the color changing, i dont think changes are necessarily bad when they go from lighter to darker....or else the other way could mean bleaching or losing the zooenthelle(sp.?) in its tissue. The RTN could be caused by several things...any new introductions of late? Make sure there is proper circulation around the acros. I find acros to be a very hardy bunch. The only time my acros did a mass die off was after a 48 hour power outage where i lost several pcs. Of course the temp dropped to below 65F without any filtering, light, or water movement.; and had a one inch thick layer of dead critters on the bottom of the tank by the time power restored. I was quite distraught. I actually did nothing by way of water changes or clean up. I simply let the algae grow over the entire tank. One month later i scraped the algae off...Voila! all my fish died but most of the acros amazingly recovered.

Cheers,
DD