LSP lost polyps on top

[DJ_PAPA]

Hi, I have some Acans that 2 months ago lost some polyps on top but other polyps stay perfet I don't understand why this happened specialy to Acans but also to some other LPS.
watter parameters are ok and light is good.
Photo:

(Those Acans in the past where fully filled with polyps on top)

On the other side I have other Acan perfectly fine in all this but it is on the othe end of the aquarium.:

Is it problems with excessive flow, or do you know what is the cause of this? (lack of some trace elements?). I feed LPS regular also.
Now that didn't happened again but I don't understand why that happened...

Thanks xD

 

[DJ_PAPA]

Hi again, any ideals help?

Greetings

 

[RtReef]

Sometimes it can happen to one colony and not to another. However have you tried to move them and give them light to moderate flow?

 

[elegance coral]

Did you change bulbs before this happened? Usually, when recession is only on the top like that, it's caused by excessive lighting. This is very common in Goniopora.

 

[Nemo4ev]

Yes I would say the light or do you have any angels? They may be nipping at the top of the acans..

 

[DJ_PAPA]

I change my bulbs from time to time but only 2/3 each time. How much time (in hours) should I have lights turned on? (430L and 430W of T5 light)

Do you think that the calcification process stopped in the mean time an that caused those problems?
Can it be a lack of some trace element?

Excessive flow? (I have vortech MP40W) Can be but in the place that they are the flow is minimum.

I actually have a Flame angel and he some times nips on a Red Acan but on those he never touches.

Greetings

 

[alowman]

did the colony that lost polyps get burned by a falling coral?