green star polyps dying

i will start off by saying that this tank is almost 10mos old and i have never lost any livestock except for a xenia which just melted away everything else is thriving.parameters as follows:
nitrate 0 to .5 but usually 0
amonia and nitrite ofcourse 0
ph 8.3 always never changes
calcium always 460
phosphates 0
dkh 8-9 usually
maganesium ? don't test for it.

my green star polyps are not green anymore but all white and don't fully extend fully out of their mat. they used to come out about 1/4 inch and flowing all green in the current, now only about less than half that and much smaller. the red mat seems to be receding from the rock in places. i had it in a smaller tank with pc lighting and is not in a 75gallon with t-5 lighting. i am thinking maybe too much light so i moved it down lower. green star polyps or xenia only problems i have had in this setup.

my other corals are:
open brain
tooth coral
flower pot (alevopora) thriving and growing
various candy canes
many mushrooms
toad stool leather (i had the gsp next to it so i moved away thinking some warfare might be going on)
hammer coral - branching type
frogspawn also branching type
kenya tree
sun coral
plate coral
as i stated before all other corals are doing wonderful.
i was wondering if the iron and maganese i dose for the flower pot could be causing the problem

any thoughts would be greatly appreciated.
thanks in advance
camera is on loan to a friend right now so no pics.

 

Tough to say since it is only coral having problems. The move away from the leather was good. Is it getting good flow? They seem to like good flow IME. You might have something on the iron and manganese. Do you use carbon? You could have a lot of allelopathic chemicals in the tank and the GSP is getting the worst of it.

 

yes carbon and chemi pure elite, and also i have had a problem with xenia.

 

how long has it been under the new lights?

I've had GSP grow behind something where it got 0 light and it bleached very white - the polyps and the mat. Anyway, it eventually grew out the other side and back into the light. It is that piece where I see similarities between us. That part was very white for a couple of months if I remember right. But eventually darkened back up. The part in the shade is still all white. Also, not sure why, but that part has stopped growing... The rest of it is still going nuts.

 

i moved it away from toadstool and lower in tank to give alittle less light thought maybe too much light.

 

what are everyone's thoughts on dosing iodine for gsp or xenia. i have never dosed iodine and xenia just melts away.

 

I always advise against dosing iodine and/or iodide. You can't really accurately test for it and it is easy to overdose but hard to have too little in the tank (i.e. you probably don't need to add any).

That's not to day an iodine dip isn't in order... but I wouldn't do it for GSP.

 

Iodine can be dosed safely. If you use a "weak" brand, the kind you find at LFS in large bottles such as Kent Marine Iodide Supplement and follow the directions adding once a week you will not over dose. I have dosed that way for years. If, however, you use Lugols', that can be over-dosed as it is much more concentrated. The fading GSP is puzzling. I would venture to say the light shock did it. Next time you want to move a coral from less intense light to more intense light, or when upgrading or changing bulbs, use the screen technique to acclimate your coral to the new light.