my coral is bleaching, why?

[Nellie]

Thanks for the tips, everyone. I'll test alkalinity and calcium today. The bulbs are about 10 months old, so maybe that's part of it. Flow seems good, but I'll double-check.

Cool, let us know what the tests say. Also, if you're gonna replace the bulbs, do it one at a time to avoid shocking the tank.

Exactly. Sudden changes are a no-go. Also, consider reducing the photoperiod by an hour or two while they adjust.

[SlateFang]

And don't forget to chill with the water changes if you're messing with the bulbs. Too many changes at once can freak everything out.

[mikoson]

One more thing, what's your magnesium level? Low mag can mess with calcium uptake, even if your calcium levels seem fine. It's all connected.

[luxion]

True, magnesium's often overlooked. Aim for around 1350 ppm. If it's low, a supplement might help stabilize everything else.