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My Duncan corals aren't extending their polyps as much as they used to. I've got them in a 40-gallon tank with moderate flow, 78°F, and 1.025 salinity. Lighting is AI Prime at 60%. Any ideas what's up?

Duncans can be picky about flow. If it's too strong, they'll stay closed. Try moving them to a lower flow area and see if they perk up. Also, check your alkalinity, they like it stable around 8-9 dKH.

Mine did the same thing when I first got them. Took a few days to adjust. Maybe they're just settling in?

SeaLord2 wrote: ↑Thu Sep 18, 2025 11:40 pm Duncans can be picky about flow. If it's too strong, they'll stay closed. Try moving them to a lower flow area and see if they perk up. Also, check your alkalinity, they like it stable around 8-9 dKH.

Yep, flow's a big one. Mine threw a fit when I cranked up the wavemaker. Chill flow and they'll thank you.

I've had luck feeding mine small bits of mysis shrimp. They're greedy little things once they get going. Maybe try target feeding to encourage them to open up.

Duncans are pretty hardy, but they do need stable params. If your alk is swinging, they'll sulk. Test your magnesium too, it should be around 1350 ppm. Also, how old are your bulbs? Older lights can mess with their vibe.

Thanks for the tips, everyone. I'll try moving them to a lower flow spot and check my alk tonight.

Duncans are chill once you dial it in. Mine love the sandbed, low flow, and a sprinkle of reef roids every now and then. Keep it simple, ya know?

Mine didn't open for a week. Then one day, boom, full extension. Sometimes they just need time.

I've heard some folks say Duncans are like the divas of the coral world. Not sure if that's true, but mine sure are picky about their spot.