Is there an upper limit for Mg ?

[karimwassef]

I've run my tank at 1600ppm for years with no ill effects. A local friend accidentally overdosed to nearly 3000ppm with no ill effects...

It keeps our Ca and carbonate from precipitating and even kills bryopsis (apparently)...

I realize that natural seawater is about balance, etc...

But is there a red line for Mg? 2500? 5000?

[mcgyvr]

From here..
http://www.advancedaquarist.com/2003/10/chemistry

Toxicity Of Elevated Magnesium
There have been very few studies on the toxicity of elevated magnesium on most marine organisms. Most toxicity studies involving magnesium use freshwater species. This is largely true because magnesium is already quite high in concentration in normal seawater, so to significantly elevate it requires conditions that would rarely be encountered in oceans or even lagoons.

Bingman12 pointed out in a previous article that at elevated concentrations (>8,000 ppm), magnesium has been used as an aid in shucking oysters, helping to force the oyster open,12-14 and also as an anesthetic for them.12 Consequently, magnesium does have potentially negative biological effects at significantly elevated concentrations.

Searching for
marine toxicity of magnesium
Doesn't yield much if any information..

[bertoni]

I've never seen any reports of problems that would indicate much toxicity for magnesium, not within anything like the levels I've seen in tanks so far. At some point, it'll cause problems, from increased salinity, if nothing else, but the limit might be very, very high.

[ssgss gogeta]

I read somewhere that 8000 was about the point of trouble can't remember where or why though


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[jason2459]

Above 1800 and my snails became extremely sluggish. Over 2000 and they started to go into like a coma. Once dropped down to around 1500 they revived. Some people have reported going over 2000 and even 2500 and believe their snails died.

[nereefpat]

The killing bryopsis effect is hard to quantify. My understanding is that this effect is seen from a specific brand of Mg product, and it was something other than the Mg that was doing the killing.

[Breadman03]

Originally Posted by jason2459

Above 1800 and my snails became extremely sluggish. Over 2000 and they started to go into like a coma. Once dropped down to around 1500 they revived. Some people have reported going over 2000 and even 2500 and believe their snails died.

I'd have to review my logs for more accurate info, but I went to something like 2300, and maybe higher. I lost a bunch of my snails and crabs and I couldn't acclimate any new ones to my system. I ended up doing several massive water changes to get MG back to normal range.

[ReefsandGeeks]

OP are you curious because you just want to know where the line is that negative effects begin, or are you trying to find out because you intend on intentionally keeping Mag higher to further push Ca levels?

[karimwassef]

I don't think there's much benefit above 1600- but now I'm curious if there is.

My purpose was to minimize testing and effort. If there's no upper bound, I can be more liberal (+10%) and not have to worry about it.

I keep my tank at 1600 but it will slowly meander to the 1400s. I'd like to just set it on a more liberal dosing schedule and let it settle somewhere between 1600 and 2000.

[ReefsandGeeks]

Of course there's the "keep everything as stable as possible" argument, but for Mag, I usually test once a month if I think about it, and if it's 1350 or lower, I'll dose over a few days until it's about 1600, then forget about it for a while. mag usage is much lower than Ca or alk, so it doesn't need as much attention. Especially since it's not directly tied to pH or anything like that. It really only seems to matter if it's over 2000 (snail and invert issues start) or under 1350 (Ca and alk levels may start to struggle to stay supersaturated to desired levels).

[bertoni]

I don't think it's necessary to maintain magnesium at 1350 ppm. The canonical ocean average is about 1275 ppm, and I ran tanks at 1100 ppm for years without trouble because the old Instant Ocean came at that level.

[karimwassef]

I like keeping it high so I can maintain Ca at or above 550 without thinking about it