Kalk Reactors robbing Magnesium from Reef Tanks, True or False?

[Ed Hahn]

Hello Boomer,
I heard a rumor. I wanted to reasearch to learn the facts about Kalk reactors. If the above is true I may want to reconsider using a Kalk reactor.
Thanks in Advance,
Ed

 

[chris&barb]

where did you hear this? what is there reasoning behind this?

 

[DonW]

where did you hear this? what is there reasoning behind this?

I think the theory is the ca precip binds up the Mg. I dont think its anything to worry about, if this is the case.

Don

 

[Ed Hahn]

So a Kalk reactor really has nothing to do magnesium depletion?

 

[DonW]

So a Kalk reactor really has nothing to do magnesium depletion?

You cant really say nothing, but not enough to worry about, I think there may even be some kalk out there that has mg in it. Kalk may cause some precip, you see this in the cloud in the water. The Mg part will redisolve in time. Maybe some of the mg that gets bound in the crud up on your heaters and things like that will be lost for good.


Don

 

[Curtswearing]

A potential sink that has been described by some hobbyists is the precipitation of magnesium by limewater (kalkwasser). Both magnesium hydroxide and magnesium carbonate have been suggested. I do not believe that either is an important process in most aquaria. Adding any high pH additive, including limewater, results in the transient formation of magnesium hydroxide. This material quickly redissolves on mixing such that the local pH drops below about 8.6.-9.0. Magnesium carbonate is a more complicated issue, as it is near its solubility limit in seawater and may quickly get coated with a less soluble magnesium calcite. These issues have been dealt with by Bingman in much greater detail, and his conclusion is that neither of these precipitates is a likely sink for magnesium.


I would suggest that an alternative way that aquaria using only limewater might become deficient in magnesium over time is that the limewater is simply not delivering magnesium to the aquarium even though it is present in the solid lime. How and why this might happen was discussed above involving the precipitation of magnesium hydroxide in the limewater reservoir. This lack of addition coupled to the ongoing removal of magnesium in calcification could lead to deficiencies in magnesium. Such deficiencies have not become extensive in my aquarium, but it does not have an especially high rate of calcification, and perhaps water changes have eliminated the problem. In any case, those using only limewater (or other systems that do not deliver magnesium) may want to occasionally check magnesium.

http://www.advancedaquarist.com/issues/oct2003/chem.htm

 

[Boomer]

Well, Curt's post pretty much spells it out but there is a small error in it and this article is old and we have since talked about the issue.

Magnesium carbonate is a more complicated issue, as it is near its solubility limit in seawater and may quickly get coated with a less soluble magnesium calcite

Often in this hobby there is a lack of understanding what the term Magnesium Calcite is. Hi Mg-Calcite is the MOST soluble of the carbonates. Many assume Mg Calcite is just a name for Dolomite, which it is not. Dolomite and Calcite are not the same mineralogical. Mg Calcite is just Calcite that has a low to high degree of Mg++ in its crystal lattice. There are two forms. Low Mg-Calcite, which is just plan old Calcite and Hi Mg-Calcite which in another beast. So it becomes tricky when you just say Mg-Calcite.

Hi-Mg-Ca ( Ca^x-Mg^y CO3 ) is the most soluble followed by Magnesite ( MgCO3, Magnesium Carbonate), Aragonite (CaCO3), L-Mg-Ca (CaCO3) and then Dolomite ( MgCa(CO3)2 )

As far as is what you are asking Ed true, Yes. But, it is not an issue for one big reason. Almost all of the media in the reef tank that is carbonate based will get coated with organics/ bacteria and will thus not be able to pull out any Ca++, Mg++ or CO3--. That means most of this loss will be abiotic, on heaters and pumps so, it is really not much of an issue. Finally the only Ca++ that binds up Mg++ is Calcite. Aragonite could care less about Mg++ as it does not fit into the crystal lattice very well. it is much more apt to pick up Sr. Most of the abiotic talking place in a reef tank is Calcite.

 

[Ed Hahn]

Thanks Boomer, Curt, Don for your time. I will look forward to using my Kalk Reactor.