Why are my corals retracting polyps?

[freshfable]

My Zoanthids and Acans have been retracting their polyps for the past two days. Water params are good, 0 ammonia, 0 nitrite, 5 nitrate, 8.2 pH, 1.025 salinity. Tank is a 40-gallon with AI Prime lighting, running 8 hours a day. Any ideas what's messing with them?

[oceana]

Have you checked your alkalinity and calcium levels? Polyps retracting can sometimes mean unstable parameters. Also, how old are your bulbs? Older lighting can cause stress.

[coastguard1]

I'd second checking alk and calcium. What's your temp stability like? If it's swinging more than a degree or two, that could sketch them out. My Duncan's did the same thing when my heater was acting up.

[florax]

My torch coral did this last week. Turned out my magnesium was low. Tested it and it was at 1150. Bumped it up to 1350 and they opened right up.

[Floraa7]

Have you checked your alkalinity and calcium levels? Polyps retracting can sometimes mean unstable parameters. Also, how old are your bulbs? Older lighting can cause stress.

Lighting's only 6 months old, but I'll test alk and calcium tonight. Temp's steady at 78, but I haven't checked magnesium in a while.

[fable95]

Yep, magnesium is huge. Also, any new fish or inverts? Sometimes they'll nip at polyps and cause them to stay closed. My clownfish was a jerk to my Zoas until I moved him.

[freshfable]

Thanks, everyone. I'll test alk, calcium, and magnesium tonight. No new fish, but I did add a cleaner shrimp last week. Could that be it?

[oceana]

Cleaner shrimp are usually chill, but it's possible. Keep an eye on it. If params are solid, it might just be an adjustment period. Sometimes they're weird for a bit after changes.

[coastguard1]

My torch coral did this last week. Turned out my magnesium was low. Tested it and it was at 1150. Bumped it up to 1350 and they opened right up.

Yeah, magnesium is sneaky like that. Easy to overlook but makes a big difference.

[Floraa7]

Any chance you've been dosing anything new? I had a similar issue when I switched salt mixes. Took a week for everything to settle.