Who Gives A Fish Forums

Thanks for the advice, everyone. I'll test alk, calcium, and Mg tonight. No new fish or inverts, but I did add a small powerhead last week. Maybe that's too much flow. I'll dial it back and see.

My Zoanthids have been closed up for two days now. Water params are good, 0 ammonia, 0 nitrite, nitrate at 5 ppm. Tank is a 40-gallon with AI Prime lighting, running 8 hours a day. I did a 10% water change three days ago, using Red Sea Coral Pro salt. Any ideas what's messing with them?