Maintaining magnesium for corals

[Blaze]

My tank's magnesium levels keep dropping fast, and my Zoanthids aren't looking great. I'm dosing Red Sea Foundation Mg, but it's not cutting it. Anyone else deal with this? Tank's a 40-gallon with T5 lighting, running for about a year. Params are 8 dKH, 420 Ca, but Mg sits at 1200. Corals are kinda pale.

[dawnfly]

Magnesium depletion can happen if your salt mix is low or you've got heavy coral growth. What's your water change routine? I'd test your fresh mix first. Also, check for precipitation, especially if you're dosing calcium and alk aggressively. My 75-gallon stays stable at 1350 Mg with weekly 10% changes using Instant Ocean Reef Crystals.

[craggy]

My tank's magnesium levels keep dropping fast, and my Zoanthids aren't looking great. I'm dosing Red Sea Foundation Mg, but it's not cutting it. Anyone else deal with this? Tank's a 40-gallon with T5 lighting, running for about a year. Params are 8 dKH, 420 Ca, but Mg sits at 1200. Corals are kinda pale.

How often are you dosing? Consistency matters more than quantity. I had similar issues until I switched to daily small doses instead of weekly large ones. My Acros perked up within two weeks.

[jinglebly]

Yep, gotta stay on top of it. I use a dosing pump for Mg now, way easier than manual. Also, what's your salinity at? Low salinity can mess with uptake. My tank runs at 1.026, and I keep Mg around 1300. Softies and LPS seem chill there.

[Fluxion9]

Is there a chance your test kit's off? I've had bad readings from expired reagents before. Maybe cross-check with another kit or your LFS.

[Blaze]

Thanks for the tips, everyone. I'll test my salt mix and try smaller daily doses. Didn't think about the test kit being sketchy, but it's kinda old. Gonna grab a new one tomorrow.

[dawnfly]

Thanks for the tips, everyone. I'll test my salt mix and try smaller daily doses. Didn't think about the test kit being sketchy, but it's kinda old. Gonna grab a new one tomorrow.

Good call. Let us know what the new kit says. Also, if you're using carbon or GFO, they can sometimes bind trace elements. Might be worth checking.

[craggy]

Yeah, GFO can be a sneaky culprit. I stopped running it 24/7 after it nuked my Mg. Now I just use it for a couple days post-water change if phosphates creep up.

[jinglebly]

Same here. GFO's great but needs a light touch. Btw, what's your alk at? High alk can make Mg drop faster. I keep mine at 7–8 dKH to balance everything.