Elevated Mg Lethal to Sea Urchins?

[NYCMikeM3]

Hi All,
Wondering if anyone can help/confirm if elevated Mg (~1500ppm) is fatal to sea urchins? I recently decided to increase my Mg levels from 1350ppm to 1500ppm over the course of 2 weeks – primarily to combat mild bryopsis and secondarily to see if there was an increased growth-rate of Coralline algae.

Sadly, within a couple days of the Mg levels hitting ~1,500ppm, I noticed Fuzz (our sea urchin; #IronicNamesAreFunny; also R.I.P.) had suddenly/abruptly lost most of his spines and died shortly thereafter. I’m pretty confident that nothing other than the Mg levels changed, and Fuzz had been in the tank for about a year. I got another urchin, drip acclimated him slowly and he also died within a day or two… It’s been about a week since Fuzz-Deux passed; everyone else is thriving (including all of the inverts).

The reason I’m concerned/curious is because there seems to be ‘a lot’ of articles where people have increased Mg to 1500+ and generally comment that the livestock is fine (no mention of mass urchin fatalities). I’m considering just lowering Mg levels back to normal, but again am wondering if that’s actually the issue. Very much appreciate anyone’s insight – thank you!


Some other background on the tank if it’s helpful (nothing is new/different other than the Mg target-level):

• ~100gal (pic attached)
• Using Neptune Trident & DOS
  • Alk 10.46 dkh
  • Ca 450ppm
  • Mg 1503ppm (increased intentionally from 1350 over 2 weeks)
• Nitrate: approximately 0 (I actually dose nitrate)
• S.G. 1.026
• PH 8.0 – 8.3
• Reactors: Carbon, GFO, CO2
• ICP results pending

 

[Huff747]

I'm no expert but I don't think the Mg killed them. I had always tested my Mg with a Sailfert kit and it was always telling me I was around 1200-1300. So I was regularly dosing a little. I got the trident, it was always telling me 1600. I've had it for about 3 months now. Sailfert still tells me 1200-1300. Did a Triton test and it came in at 1600. And I've got 3 tuxedo urchins that haven't skipped a beat. I'd imagine if the Sailfert test is at least consistent that I've always been running this high. It's now down in the high 1500s as I'm not dosing it any longer but the urchins are still doing their thing.

 

[NormanB]

Sorry to hear about Fuzz, however I don't think it was the Mg level.

I have an urchin and Mg levels have been at 1500+ for a few weeks several months ago with no negative impact. Mr. Prickles is alive and well.

 

[theMeat]

Have had mag up to 1600 for months to rid bryopsis a few times with no visible harm to tuxedo or pin cushion urchins

 

[Cory]

What product did you use to add magnesium? It might be an impurity.

 

[NYCMikeM3]

What product did you use to add magnesium? It might be an impurity.

firstly - thanks everyone for replying. I used Red Sea Foundation C to raise. I also got back my ICP results which look very clean (and confirm approximately the same Mg levels as triton is reading). The only 2 things slight off on the Icp are 20ppm Al and approx 0 nitrates. The aluminum I’ve been running metasorb and cuprasorb (I have no idea where it’s coming from - it’s also been on my Icp results sporadically since sept of last year. So I don’t think it’s Al either... it’s just the only parameter that’s off)

im officially stumped since the ICP results didn’t turn up anything else and I’ve had no subsequent issues with any of the other livestock (fish,coral or inverts).

And I definitely miss seeing what new random thing fuzz has decided to pick up and carry — but I don’t want to risk another until maybe a few more H2O changes

 

[Cory]

How fast did you add the magnesium?

 

[NYCMikeM3]

How fast did you add the magnesium?

I did it over the course of about two weeks (about a 10ppm/day increase). My Mg is down to 1450 now and I’m going to slowly take it back to around 1350 (and use Kent Mg — which seems to be the trick for bryposis anyway... sounds like it’s not the Mg so much as the “other stuff” in Kent)

I actually had an emerald crab die today too (Jacques...not exactly an ironic name but he was one of the “OG”). None of the other hermits, shrimp, coral or fish are acting strange. In fact I was gone for the weekend and the coral has noticeably grown.

very upsetting. I hate having something die, but I’m at a complete loss.

 

[Cory]

Have you checked ammonia? Sometimes ammonia is the problem with magnesium.