Ya, that's my original thought, irritation from the turbidity. I swear I'm losing 30% of my light to the dust cloud!

Darren, pretty sure it's not fish, I have mostly large tangs and a couple of large wrasses, 4 clowns. No known coral nippers.

Polyp extention
 

I had massive extention in most of my Sps colonies for a long time and then they just stopped! I tried every thing and finaly narrowed it down to a small voltage leak. I spent 14 bucks on a Rid Volt and within hours the extention was back!
It could be different problem for you but only $14 dollars out of pocket to try.
Keith.

Keith, not a bad idea. I just browsed the tank and noticed that some pieces do have good PE, especially a newly mounted pink lemonade. Pocci colonies all have great extension, as do the birdnests. But some colonies have nothing at all. For 14 bucks, I'll try grounding the tank.

Interested to hear the result of that.. Tagging along.

Haven't seen a whole lot of reefs in the wild but the ones I have seen, have all been in the daytime, and I don't ever remember thinking "Boy the polyp extension on these acros is not very good. I wonder if it's better at night time." Everything I've ever seen has all had PE to some degree, acros, porites, etc and eieio, but that said I've never seen the shagginess of a typical prostata or milli. So whether that's because maybe I never saw a prostata or milli where I've been, or if that's just not a natural occurrence, I can't say..

Tony, the wild milliporas I've seen didn't appear to be super fuzzy like we see them in tanks, if I recall. I wasn't paying a lot of attention to PE, more the size of some of the wild colonies!

But in my tank, for instance, my abrolhosensis isn't the typical bushy stick you normally see, you can actually see the body of the coral. The first three months, you couldn't tell if it was one branch or three!
The grounding probe idea has merit, and they're 12 bucks locally. I'll try that tomorrow.

The reason i think its potassium is after i dose k balance in the tank the pe is wild might be similar to after feeding the tank tho and the corals are just trying to absorb as much as possible.

do you feed any kinds of coral type food?

Hmm, might give that a try.

No, I feed the fish heavily and figure that's enough.

I've always wondered about this too, particularly in regards potassium dosing and PE. I've always been suspect that K makes the polyps extend by a physiological response rather than their own natural accord as potassium, for most animals, regulates muscle responses and fluid pressure balances between tissues. So dosing K might just be causing them to puff up like balloons... but really I don't know that for sure, so at this point I'm talking out of my a$$.

As for some colonies having PE and some not... I am suspecting an irritant, though figuring out what that may be could take forever. I'd venture to say it's probably sand that is bothering them.

Since I've been curious about this as well, I tell ya what... I've got some time to kill today while waiting for an experiment to finish. I'll dig into some journal articles and see if I can't get some sort of definitive answer.