I've had these zoas in my tank for almost 2 months now, neon greens from sea life inc, and they seem quite healthy. There's quite a few more than there were when I started, the polyps are bigger and very colorful, and everything opens like clockwork with the lights and seems to be doing great. They were initially in the sand bed, but I ended up anchoring some later because they kept getting pushed around, though one large clump seems to have made the sand bed and a little piece of rock work well together, and they have stayed in place nicely.

My only concern is their length..... the polyps open to probably a half an inch or so including the skirt, but the longest stalks are probably an inch and a half long. The stalks are semi-transparent (taller portions are more colored, I think this is just because the stalks are shaded), but these zoas look more like goniopora when their heads close up at night.... and it bothers me. I've heard that this is often associated with low light conditions, but I'm not sure they qualify for that: they're in a 7.5G display with 36W of T5, 11" from the fixture and about 8 of those inches are through water. They are not in the shade.

Should I be concerned? Should I expect my newer zoas to reach long lengths in the coming months? From everything I can tell they are healthy, and when the heads are open you can't tell the length at all, it just looks like they're covering a rock, though at night it's like a forest.

mine do that when they are more in the shade and do not have enough light.

Those that are closer to the light tend to be very very short and those that are in the shade will extend a lot more.

put them in higher flow and move them up in the tank, that should resolve the stalk length if they're zoas.

If they look happy and are opened up I'd just leave them. I have some zoas and palys under MH lighting and the ones in the sand bed reach up. Some move well, but some will get irritated and close up. It depends on the species. If your worried try to move a few of them up and see how they do. In that case they get pissed and close up you don't have to stress all of them out.

Thanks for the replies, because I don't think it's a lighting thing and because they seem fairly rooted in place, I'll tilt the powerhead a little to give them a little more substantial flow and see how they like that. Still not a lot, but because of a little rock ledge above them towards the powerhead, the flow they've been getting is probably not that strong. This is them before the lights go on:

Probably is the light. Mine are placed in the same situation as yours but under 96w of t5.

+1 the light