Magnesium Levels

Shaun Sweeney · Mar 24, 2018

Greetings all. I'm just wondering if anyone can suggest an answer to my Mg level issue that has remained at about 1500 for several weeks - in spite of the fact that it has been a long time since I turned the dosing pump off. I've double checked and there isn't any siphoning happening. Any ideas?
Many thanks .... Shaun

Crabs McJones · Mar 24, 2018

Shaun Sweeney said:
Greetings all. I'm just wondering if anyone can suggest an answer to my Mg level issue that has remained at about 1500 for several weeks - in spite of the fact that it has been a long time since I turned the dosing pump off. I've double checked and there isn't any siphoning happening. Any ideas?
Many thanks .... Shaun

Are you doing water changes? If so how often and how much? And what salt mix are you using?

Shaun Sweeney · Mar 25, 2018

I do weekly water changes but since my system is about 375 gallons I don't usually get more than about 10%. I use local ocean water which only requires minimum addition of salt and I use Reef Crystals. I plan a solid 20% water change sometime this week.

Crabs McJones · Mar 25, 2018

Shaun Sweeney said:
I do weekly water changes but since my system is about 375 gallons I don't usually get more than about 10%. I use local ocean water which only requires minimum addition of salt and I use Reef Crystals. I plan a solid 20% water change sometime this week.

Do you know the mag levelsof the water you're adding? #reefsquad

Shaun Sweeney · Mar 25, 2018

Yes, I've checked it several times and the really neat thing is that after I add the salt, all levels come right into line. In particular, Mg ends up around 1380.

Randy Holmes-Farley · Mar 25, 2018

If magnesium really is high (testing is often off, and the Red Sea kit in particular causes issues for many folks), then the only way to reduce magnesium is by water change.

How are you supplementing calcium and alkalinity?

A 10% water change with 11380 ppm magnesium with a tank at 1500 ppm will drop magnesium to 1488 ppm, so the decline will be slow.

Randy Holmes-Farley · Mar 25, 2018

Shaun Sweeney said:
Yes, I've checked it several times and the really neat thing is that after I add the salt, all levels come right into line. In particular, Mg ends up around 1380.

You are saying it rises on its own after a change?

That is likely only if salinity is being allowed to rise due to evaporation. Magnesium doesn't rise on its own if you are not adding it.

Shaun Sweeney · Mar 25, 2018

Thanks for the replies. The Mg doesn't rise on it's own. It krept up several weeks ago and just hasn't come down. I use the Salifert test kit. I think I pushed it up with my dosing (and I've done that before) but traditionally, it has slowly come down when I quit dosing. My salinity stays bang on and stable with the auto top off system.

estebanb450 · Mar 26, 2018

I had some issues a few weeks back and my mg was high over 1600 with the Red Sea it’s been about 3 weeks tested today and I’m still over 1600ppm with a Red Sea kit today it used .98 of the reagent and it turned blue.
50 gallon total water volume

Might take a while if you let it drop on it’s own depending on your coral load

Randy Holmes-Farley · Mar 26, 2018

Shaun Sweeney said:
Thanks for the replies. The Mg doesn't rise on it's own. It krept up several weeks ago and just hasn't come down. I use the Salifert test kit. I think I pushed it up with my dosing (and I've done that before) but traditionally, it has slowly come down when I quit dosing. My salinity stays bang on and stable with the auto top off system.

OK, then water changes, preferably with a lower magnesium mix, is the only way to lower it. You might try normal IO for a while since I think it is a bit lower than RC.

Shaun Sweeney · May 13, 2018

Figured I should put this one to bed. Finally figured out the high Mg levels. They were coming from a Fluval filter canister that I had used lava rock in. The lava was leaching Mg. Threw it out and the levels settled in again. Thanks for all the comments.

Randy Holmes-Farley · May 14, 2018

OK, thanks for the update.

Newb73 · May 14, 2018

What are the real negative effects of running high Mg though?

I some times run my mg up to 1500 to 1600 and I see more positive effects than negative.

Randy always corrects my anectodal stories but I consistently see less algae and better looking softies w higher mg levels. My SPS (monti, acro, birds etc. And fish seem mostly unaffected).

I know its bad for snails and clams above 1700 right??