Magnesium question

[jerthunter]

I have never tested Mg in my tank and the only reason I am thinking about it now is that my current batch of Kent seasalt is testing at 500 ppm Ca and 2.0 dKh. I have been adding reef carbonate to raise my dKh. From what I have read Mg is important for calcium levels but I haven't been able to find what it actually does. From what I have read it sounds like magnesium is needed to keep high calcium levels so would I be right in assuming with 500 ppm Ca that my Mg is high as well?
Sorry to be asking these questions but everything I have read so far just mentions magnesium as being important but I don't know for sure why.

 

[drew2005]

Originally Posted by Jerthunter
I have never tested Mg in my tank and the only reason I am thinking about it now is that my current batch of Kent seasalt is testing at 500 ppm Ca and 2.0 dKh. I have been adding reef carbonate to raise my dKh. From what I have read Mg is important for calcium levels but I haven't been able to find what it actually does. From what I have read it sounds like magnesium is needed to keep high calcium levels so would I be right in assuming with 500 ppm Ca that my Mg is high as well?
Sorry to be asking these questions but everything I have read so far just mentions magnesium as being important but I don't know for sure why.
Magnesium prevents calcium from precipitating to fast. Without proper magnesium levels of 1300-1350 your calcium its hard to increase. It can also help stabilize ph and alkalinity.

 

[jerthunter]

Originally Posted by drew2005
Magnesium prevents calcium from precipitating to fast. Without proper calcium levels of 1300-1350 your calcium its hard to increase calcium levels. It can also help stabilize ph and alkalinity.
Thanks, so if I have high calcium and low alk I can be relatively sure that my mg isn't low?
Also is there any problem with what I am currently doing, adding reef carbonate, to raise my alk?

 

[drew2005]

Originally Posted by Jerthunter
Thanks, so if I have high calcium and low alk I can be relatively sure that my mg isn't low?
Also is there any problem with what I am currently doing, adding reef carbonate, to raise my alk?
Its possible. I would definitely test for magnesium. Especially if its a reef tank. Are you adding the reef carbonate to the make up water or to the main tank?

 

[turningtim]

From what I understand the Mag level is important for the absorbsion of CA. If you don't have the correct Mag level you can have as much CA as you want and will not do any good.
I would be very concerned that your salt is reading that low in Alk! Have you double checked with another test kit? It just seems that 2.0 dkh is off the charts low.....
HTH
Tim

 

[jerthunter]

Originally Posted by drew2005
Its possible. I would definitely test for magnesium. Especially if its a reef tank. Are you adding the reef carbonate to the make up water or to the main tank?
Well it is turning into a reef tank, I have Xenia, some zoos and a mushroom. I suppose eventually I will break down and buy a Mg test but I will wait for awhile since I haven't had any problems with my calcium levels.
I add the reef carbonate to my make up water, and also to my water change water since my salt mix has low alk levels.

 

[jerthunter]

Originally Posted by TurningTim
From what I understand the Mag level is important for the absorbsion of CA. If you don't have the correct Mag level you can have as much CA as you want and will not do any good.
I would be very concerned that your salt is reading that low in Alk! Have you double checked with another test kit? It just seems that 2.0 dkh is off the charts low.....
HTH
Tim
No, haven't doubled checked it with another test kit but it makes sense to me, I started using the current bucket of Kent sea salt without testing my alk and I noticed a rapid decline in my coraline growth. When I tested my tank I noticed my dKh was around 6.0 if I remember correctly which prompted me to test a fresh batch of saltwater which is how I found my dKh was low.
If Mg is needed for proper Ca absorption then I suppose I should worry about it more but so far from what I have read it appears that it serves to prevent calcium and carbonate from precipitating.

 

[turningtim]

But doesn't that logic follow? If it doesn't precip then it can be absorbed? :thinking:
I would get that Alk double checked and if its coming out of the bucket at 2dkh, I would take it back or call Kent. Thats just crazy! Could have gotten a bad batch been know to happen....
HTH
Tim

 

[reefnut]

Originally Posted by Jerthunter
If Mg is needed for proper Ca absorption then I suppose I should worry about it more but so far from what I have read it appears that it serves to prevent calcium and carbonate from precipitating.
Magnesium does NOT prevent calcium and alkalinity from precipitating. As mentioned, it effects how much calcium the water can hold. IMO the three "major" tests that need to be done in a reef system is calcium, alkalinity and magnesium, in addition, additive are often needed to keep the three in line.
I would also recommend getting a second opinion on your test results.

 

[jerthunter]

Ok, that makes sense but here is my situation, my Calcium tests right at 500 ppm, so unless I am getting a bogus reading of calcium my Mg should be ok?
What I am trying to determine, mostly for my own piece of mind is if Mg helps with the absorption of Ca (I.e. I could have 500 ppm of calcium but it would be unuseable) or if helps with the absorption of calcium by allowing more calcium to remain dissolved in the water. It sounds like it is the second one. Which right now makes me THINK that my magnesium is not low.
Thanks for the advice, I will try to get a second opinion on the alk.
I was thinking that the Mg would for a complex with the carbonate ions which could be the explaination as to how it helps more maintiain higher calcium levels. But whatever the reason I think I got the answers that I need for now...
Thanks again.