polyps receding

[Floyd R Turbo]

Just for the record, after having a discussion with someone with vast knowledge, there is a huge unknown when it comes to PE. No one really knows what causes it and why. So claiming that the corals are "full" because the polyps aren't extended is a HUGE maybe. So let's stop short of calling it fact until it's well documented, otherwise that's grounds for calling BS. Just because X led to Y doesn't mean that is the answer. Just saying.

[Ace25]

I agree with Floyd. Out of all the different things that could cause poly retraction, only 1 is positive (they are full and don't need to catch food) BUT there are a lot of negative things that could cause polyps not to extend. To make a blanket statement that the corals are full is at the very least bad advice, but could be deadly advice if the corals are hurting due to other reasons and you do nothing to correct the issue. Since you say you are running Rox carbon, I highly doubt the issue is 'corals are full' as the carbon really strips out a lot of stuff from the water. Carbon should create the opposite effect, polyp extension, if the issue was food related.

Since none of us know your system, parameters, daily routine, none of us can say with any certainty what the exact issue is, so take all advice with a grain of salt and do your own testing to figure out the cause and solution, and if you figure it out please post what you find. One thing that stands out is you say you had low alk and raised it up to 8. What was your alk before and how quickly did you raise it? What was the parameters in your friends tank that you put the corals in? Switching tanks with different parameters can cause SPS corals to suffer as they take much longer to acclimate to new parameters. Regardless, 3 weeks without polyp extension is bad for SPS corals.

[SantaMonica]

I actually don't think it's too much food, but just that it could be. Otherwise corals on a reef would not need to open.

[Amphiprion]

It's a bit different on reefs, since many corallivororous fishes are diurnal.

I agree that many factors affect polyp extension in general and that polyp extension or lack thereof can mean many things.

[RkyRickstr]

If you are not using a skimmer the carbon absorbs way more organic material. When it started happening me I switched the carbon weekly. I also read somewhere that carbon looses effectiveness after a few days because it gets covered in slime like everything else in your tank and at that point it just becomes more biological filtration. So now I run small amounts of carbon and change weekly. I can see the difference in water clarity. Much better.