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I've noticed my coral expelling zooxanthellae over the past few days. Water params are good, 0 ammonia, 0 nitrite, nitrate at 5 ppm, salinity 1.025, temp 78F. Lighting is AI Prime HD, running at 70% for 8 hours. Tank is a 40-gallon breeder with a protein skimmer. Any ideas what's causing this?

Zooxanthellae expulsion can be due to sudden light changes or stress. Have you adjusted your lighting recently? Also, check for any spikes in phosphate or alkalinity. My Acropora did this when my alk jumped from 8 to 11 dKH overnight.

Yo, sounds sketchy. Maybe your coral's just vibin' wrong. Did you mess with the flow lately? My zoas freaked out when I swapped my powerhead. Also, how old's your salt mix? Old salt can mess with stuff.

motortune wrote: ↑Mon Aug 04, 2025 12:51 pm Yo, sounds sketchy. Maybe your coral's just vibin' wrong. Did you mess with the flow lately? My zoas freaked out when I swapped my powerhead. Also, how old's your salt mix? Old salt can mess with stuff.

Flow changes can definitely stress them. What's your current setup? I've seen this happen with too much direct flow on LPS.

It could also be a temperature fluctuation. Even small swings can cause stress. Do you have a heater controller? My tank dropped to 76F last winter and my corals bleached a bit.

Yep, temp swings are bad news. My buddy's tank crashed when his heater stuck on. What's your pH like? Low pH can mess with zooxanthellae too.

Thanks for the suggestions. I haven't changed the lighting or flow recently. My pH is stable at 8.2, and the heater's on a controller. I'll test phosphate and alk again tonight.

fairylife wrote: ↑Mon Aug 04, 2025 5:21 pm Thanks for the suggestions. I haven't changed the lighting or flow recently. My pH is stable at 8.2, and the heater's on a controller. I'll test phosphate and alk again tonight.

Good call. If everything checks out, maybe try reducing light intensity by 10% for a few days. Sometimes they just need a break.

If it's not the lights or flow, maybe your coral's just being dramatic. Mine do that sometimes. Chill for a bit and see if it bounces back.

Dramatic or not, keep an eye on it. If it worsens, consider a small water change with fresh salt mix. Sometimes that resets things.