# magnesium



## Daniel Thornberg (18 Oct 2015)

Hello
Since I started reading in here been more aware that I need to add Mg. 
But here it says to use MgSO4 but I got wrong once and got MgCI2 instead .
Got told it does the job aswell but are a bit stronger then MgSO4.
Atm I been dosing  on free hand since I don't know exakt amount I should.
And never seen it bobble this much before from the plants

Was I told the right it works the same ?
Since I found 25 kg bag really cheap.
So the question is how much should I dose in a 720l tank?


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## dw1305 (19 Oct 2015)

Hi all,


daniel Thornberg said:


> But here it says to use MgSO4 but I got wrong once and got MgCI2 instead .
> Got told it does the job aswell but are a bit stronger then MgSO4.


It will be the hexahydrate, so MgCl2.6H2O.

The RMM is 203 g mol-1, and the RAM of MG is 24 g mol-1, so ~12% Mg. This means that you can use the same amount  as you would MgSO4.7H2O.

cheers Darrel


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## Daniel Thornberg (19 Oct 2015)

Thanks so about same amount and problem with it


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## Manuel Arias (19 Oct 2015)

dw1305 said:


> It will be the hexahydrate, so MgCl2.6H2O.
> 
> The RMM is 203 g mol-1, and the RAM of MG is 24 g mol-1, so ~12% Mg. This means that you can use the same amount as you would MgSO4.7H2O.



Well, I do not want to be pedant here but:

MgCl2.6H2O is 203.32 g mol-1
MgSO4.7H2O is 246.5 g mol-1

Mg is 24.30 g m-1

So the relative concentration in mass of Mg in each molecule is 11.95% and 9.86%, so there is a difference in concentration of approx 2.1% in mass between one form and the other. To have a right dosage when moving from MgSO4.7H2O to MgCl2.6H2, you have to apply a correction factor in the weights of 0.825 (or 1.121 if you do it in the other direction), i.e. per each gram that you were adding previously of MgSO4.7H2O, you have to add instead 0.825 grams of MgCl2.6H2O to keep fix the proportion of Mg in the mix you are adding. Considering that Mg affects to the gH and the role of this parameter, it is not really critical the difference, but it might be important.

By the way, Chloride is a trace element for plants, but also an electrolyte in fishes and invertebrates. Too high levels of Chloride are not optimal for the livestock as will interfere in the osmoregulation as well as the neurons , so  I would be a bit careful about using it in tanks with something more than plants. Here there is an article about toxicity of it in different freshwater pools, and some fishes for instance have tolerances so low as 3 ppm:

http://www.uri.edu/ce/wq/ww/Publications/Chlorides.pdf

Just for the record, 3 ppm means 3 mg/l. Depending on the volume of your tank and the amounts you are adding of MgCl2.6H2O, it is easy to compute how many ppms of Cl are you introducing in your tank, not considering other factors of course, like the use of tyosulphates to remove chlorine form your tap water (if you do it) or the compensation you do when changing water, of course.


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## dw1305 (19 Oct 2015)

Hi all, 





Manuel Arias said:


> So the relative concentration in mass of Mg in each molecule is 11.95% and 9.86%, so there is a difference in concentration of approx 2.1% in mass between one form and the other.


Manuel, honestly it doesn't make any practical difference.

You just need some magnesium, it isn't toxic, and we don't really know how much we need.  All the suggestions for levels are just that "_suggestions_", they are "_best guess_" figures at best.

I've never attempted to measure how much magnesium there is in my tank water (I work in a lab. with an AAS etc., and the tanks are in the teaching lab. next door ), in fact I don't measure any water parameters other than conductivity, which I keep at about 100 microS (I keep soft water fish).

My tanks are sometimes magnesium deficient, have a look at the <"Duckweed Index">, it explains this as a method. 





Manuel Arias said:


> I'm not a chloride fan either, but I think you can ignore this small amount. Have a look at at Joe Gargas' article <"Water Chemistry: Osmoregulation, Ionic Imbalance & pH">, article starts on page 7.


cheers Darrel


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## Manuel Arias (19 Oct 2015)

dw1305 said:


> I've never attempted to measure how much magnesium there is in my tank water (I work in a lab. with an AAS etc., and the tanks are in the teaching lab. next door ), in fact I don't measure any water parameters other than conductivity, which I keep at about 100 microS (I keep soft water fish).



I do not try, either. Of course it is just un estimation, and that is why I also commented in my that I truly believe that the error has no impact, and also why I labelled my post ad pedant at some point.

However, Mg is a macronutrient, even if we do not know the exact dosis or we make a mistake of 2% is not going to be a problem. But adding Cl as part of a macronutrient, when Cl is in fact a micronutrient, it can have impact in the organisms like fishes, and my answer expressed more concern about that than about the dosage of Mg.


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## Daniel Thornberg (19 Oct 2015)

So in other words keep dosing low with this since to high dosing aint good for fish and shrimps.

Will look harder to find MgSO4 then since its vetter


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## Jake101 (19 Oct 2015)

Hi Daniel,

This guy is selling EI dry salts in Sweden. I have been ordering from him, good service. 

http://www.haack.se/pmdd/index.php?option=com_content&view=article&id=20&Itemid=53


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## Manuel Arias (19 Oct 2015)

daniel Thornberg said:


> Will look harder to find MgSO4 then since its vetter



I would say yes, but that depends on you. If you are not using other sources of Cl and your dosis of MgCl2 is not much, then it could be fine, but as many things in life, I think is always better have some safe rules when adding products to the tank. This is, of course, just my point of view. Others can tell different.

To help you, I can do some figures here:

Cl is 35.45 gr  mol-1 so, in a gram of MgCl2.6H2O there are approx. 0.35 gr of Cl. Considering a tank of 100 litres, then adding a gram of MgCl2.6H2O will introduce a total of 3.5 ppm, assuming all the MgCl2 is dissolved into the water, which will happen as MgCl2.6H2O has a solubility of 167g / 100 mL. The same amount in your tank of 720 l raises the Cl levels to 0.49 ppms, which I will say is safe. of course, if you add 2 grams you are doubling the Cl concentration, and 3 grams will imply 3 times that. As mentioned by dw1305, there is no much difference in the amounts when goes to use MgSO4.7H2O or MgCl2.6H2O, so we can use the usual rules of 3:1 proportion in gH booster plus the rule of 16 gr per 80 litres to see that the target levels of Mg in relation to the desired dgH will go to around 36 gr of MgCl2.6H2O to achieve equivalent levels per each increment of 1 dgH in your tank, which is quite a lot of Cl, becoming quite salty your water and clearly unsafe for freshwater life.

Hope this help to understand the problem.


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## ian_m (19 Oct 2015)

daniel Thornberg said:


> Will look harder to find MgSO4 then since its vetter


Magnesium Sulphate is commonly available from Ebay and most Chemists/drug store/pharmacy. It is used as a foot & bath soak. Also available in garden centres, thought generally rather expensive 25Kg bags. From Ebay 25Kg will cost about £15.

http://www.boots.com/en/Westlab-Pure-Mineral-Bathing-Epsom-Salt-1-Kg_1546590/


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## Daniel Thornberg (19 Oct 2015)

Jake101 said:


> Hi Daniel,
> 
> This guy is selling EI dry salts in Sweden. I have been ordering from him, good service.
> 
> http://www.haack.se/pmdd/index.php?option=com_content&view=article&id=20&Itemid=53



Thanks I know .
Just tried to find it cheaper.
They sell for about 25-30kr for 100g while I found a bag of this other Mg for 99kr for 25 kg 
It's hught diffrent since I use a fair bit on my 720l tank


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## Daniel Thornberg (19 Oct 2015)

Manuel Arias said:


> I would say yes, but that depends on you. If you are not using other sources of Cl and your dosis of MgCl2 is not much, then it could be fine, but as many things in life, I think is always better have some safe rules when adding products to the tank. This is, of course, just my point of view. Others can tell different.
> 
> To help you, I can do some figures here:
> 
> ...


Thanks it's alot to take in but in the end I understand it aint good in long run.
I will dose about 30-40gr to I find MgSO4 to replace it.
It should be rather safe with this small amount


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## Daniel Thornberg (19 Oct 2015)

Th


ian_m said:


> Magnesium Sulphate is commonly available from Ebay and most Chemists/drug store/pharmacy. It is used as a foot & bath soak. Also available in garden centres, thought generally rather expensive 25Kg bags. From Ebay 25Kg will cost about £15.
> 
> http://www.boots.com/en/Westlab-Pure-Mineral-Bathing-Epsom-Salt-1-Kg_1546590/


Thanks  will look on ebay


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## Daniel Thornberg (20 Oct 2015)

So been ordering 1.5kg MgSO4 now .
Since I still got magnesium chloride I will mix those with just a small amount chloride so I don't have to throw it away


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