Can an SPS still grow with little to no polyp extension?

[NigeltheBold]

I've got a reef tank with several SPS frags and a few fish, including a moorish idol that I've had for about 6 months (he eats like a pig). Some of my sps are growing well, like my Hawkins echinata, purple Stylo and my bird of paradise. However, I haven't had much luck with other Acropora like tenuis and tort. I have a small Oregon tort frag that I've had for about a year. It has great color, but I never see polyp extension and it hasn't grown at all. Any time I try to add a tenuis frag, it never extends it's polyps and doesn't seem to do well. I have a feeling the moorish idol is nipping at the polyps, but I find it strange that he doesn't touch the polyps on the bird's-nest or purple pocillopora. He may be targeting new frags... I don't know.

Anyway, my question is, will coral growth slow or stop if a coral can't extend it's polyps? And if a color still has color, but I never see polyps, does that mean that it's still alive and doing okay?

 

[Bribo12]

Usually polyp extension means happy. However these corals don’t put polyps out during the day usually due to predators and only put them out at night to feed. Have you looked for PE at night, usually it’s a lot crazier than during the day.
If it still has color it may be alright, coral growth can stop for many reasons though.

 

[NigeltheBold]

Usually polyp extension means happy. However these corals don’t put polyps out during the day usually due to predators and only put them out at night to feed. Have you looked for PE at night, usually it’s a lot crazier than during the day.
If it still has color it may be alright, coral growth can stop for many reasons though.

I haven't checked at night when the lights are off, but I will.

 

[jda]

The only time that they polyps HAVE to be out is for gas exchange. This is why they are out at night when photosynthesis is not happening, when in bags or when flow completely stops. I would concentrate more on color and growth, but pay attention to PE as an indicator of change... if a normally hairy corals is now all closed up, then investigate just like if a normally low PE coral now has a ton, then they could be struggling to exchange gas (like ammonia is too high, or something).

Mine don't have a ton, but they don't have nothing either. There are photos in my rebuild thread of the type of PE that I have the corals grow as fast as anybody's, even those with more PE.