# Dosing Magnesium



## Dale (May 26, 2004)

Hello,
Our water analysis indicates that our water has 8ppm magnesium. Chuck Gadd's calculator indicates that the range should be in the order of 5-10ppm. I change 50% of the water once a week (Barr Method). Do I need to dose magnesium due to uptake by the plants and if so, how much for a 35 gal. tank.
Thanks,
Dale


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## JLudwig (Feb 16, 2004)

Dale said:


> Hello,
> Our water analysis indicates that our water has 8ppm magnesium. Chuck Gadd's calculator indicates that the range should be in the order of 5-10ppm. I change 50% of the water once a week (Barr Method). Do I need to dose magnesium due to uptake by the plants and if so, how much for a 35 gal. tank.


Hey Dale... this prolly depends on your calcium levels, 8 would be great if your GH was around 30 ish, which would be 2 or so. You want a 3:1 ratio Ca to Mg, I wouldn't mess with it really....

Unless you're not dosing that much iron and are seeing iron deficiency, IIRC Mg deficiency can look like iron problems...

Jeff


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## Edward (May 25, 2004)

Hi Dale,

Mg of 8 ppm makes 1.8 dGH. Usual Ca:Mg ratio is about 2:1 to 4:1, so your proper Ca should be 16 - 32 ppm and that would come to a total dGH of 4 to 6.
What is your dGH?

Edward


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## Dale (May 26, 2004)

Edward,

Based on my test kit, my GH is 120ppm (6.72dH). KH was 80ppm. Our water analysis is 34ppm Calcium. Hope that helps.

Dale


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## Edward (May 25, 2004)

It's a match,

34 ppm Ca / 7 = 4.86 Ca dGH
8 ppm Mg / 4.4 = 1.82 Mg dGH

4.86 Ca dGH + 1.82 Mg dGH = 6.68 total dGH

6.68 total dGH x 17.86 = 119.3 ppm dGH

Your Ca:Mg ratio of 4.25:1 is so ideal you don't need to dose any Mg.

Edward


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## Dale (May 26, 2004)

Thanks for your help. One less fertilizer to worry about!


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## bonklers (Sep 24, 2005)

*A few questions:*

What's the reason behind Ca:Mg ratio of 2:1 - 4:1? Or where can I read about it.
What will happen if the ratio is very far off, will I get Ca/Mg deficiency depending on which 'side' the ratio is overshooting?

I am currently dosing 3 grams of CaSO4 every other day on my 75 planted tank, and MgSO4 PPS style daily hoping that my curled leaves (Ca deficiency) and showing greenish nerves with yellow leaves (Iron&Mg deficiency) will go away. I'm now at my 2nd week and see no changes instead of more hair algae on my window.

Can adding too much Mg have negative effects?
Say if I want to know the ratio, what is the best option to do: buying GH and Ca test kit or GH and Mg test kit (I already have an equipment to measure uS)?


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## plantbrain (Jan 23, 2004)

Having written two exhaustive articles specifically on both Mg and Ca respectively, I've never found any evidence to date both inn practical experience nor in any literature or horticulture that suggest there is an "ideal ratio" really. As long as one does not become limiting, things should be fine.
This is true for most nutrients.

Regards, 
Tom Barr


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## MrSanders (Mar 5, 2006)

> Unless you're not dosing that much iron and are seeing iron deficiency, IIRC Mg deficiency can look like iron problems...


Jeff would you be able to explain a little more about Mg deficiency looking like iron problems? Ever have ant issues like that in your tanks that you could share about? i have had pale new growth for a while now, light very thin new leaves coming in, and then bright red stems at the tips of my stem plants .....kind of looks like an iron issue.... though no matter how much added things dont green up, at one point I was adding 10 mls of flourish Fe every day to a 60 gallon water colum tank.... didnt help....

Thanks


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## BSS (May 2, 2006)

plantbrain said:


> Having written two exhaustive articles specifically on both Mg and Ca respectively, I've never found any evidence to date both inn practical experience nor in any literature or horticulture that suggest there is an "ideal ratio" really. As long as one does not become limiting, things should be fine.
> This is true for most nutrients.


Man, I like to hear that. I've been pondering that on and off for a while. If one keeps an ample supply of all nutrients in a tank (okay, so maybe one always becomes the limiting one, but...), why should the ratios matter? I was wondering if it dealt with probability of contact with plant or what. Saying there is no ideal ratio, makes sense to me.

I like it  ,
Brian.


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## plantbrain (Jan 23, 2004)

Well, I do think "a range" is a better idea and concept for folks.
Ratios just try and get folks to add enough, they are not really meaningful, the range on the other hand is meaningful and describes *much better* the varibility within the plant cells, whole plant, tank etc. Plants, tanks, cells are not static.

But if you vary one range, you also vary others, so the ratio quickly breaks down as far as a concept.

I suppose a ratio 1:4-100, may work, or might not be 1:1?
Or 10:1, not 1:10?

You can have a NO3 of 2ppm and PO4 of 2ppm, likewise you might have a NO3 of 40ppm and a PO4 of .2ppm, but it's hard to maintain those low near limiting levels. Some folks hit the balance, some for awhile, some with less lighting, do well.

We can add different ratios and have similar plant growth over a wide range.
I think it's helpful to think about each nutrient and the effect of it's range, the ranges are quite large.

These ranges also explain the wide range of nutrient combos that do well for the plants. Ratios on the other hand, do not.

Regards, 
Tom Barr


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## Edward (May 25, 2004)

bonklers said:


> What's the reason behind Ca:Mg ratio of 2:1 - 4:1? Or where can I read about it.
> What will happen if the ratio is very far off, will I get Ca/Mg deficiency depending on which 'side' the ratio is overshooting?
> 
> I am currently dosing 3 grams of CaSO4 every other day on my 75 planted tank, and MgSO4 PPS style daily hoping that my curled leaves (Ca deficiency) and showing greenish nerves with yellow leaves (Iron&Mg deficiency) will go away. I'm now at my 2nd week and see no changes instead of more hair algae on my window.
> ...


The actual ratio doesn't matter. You need to get the cheap local fish store Hagen Nutrafin GH and Ca test kits and find out what Ca and Mg is in your tap and in your aquarium. Then you will know what is going on. This 'deficiency symptom' picture identification doesn't do any good.

Mg needs to be dosed daily just like the other nutrients. Ca is different. You need to add enough Ca to reach 20 - 30 ppm. This concentration will not change for many weeks.

Edward


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## kekon (Aug 1, 2005)

I've just had Ca = 24 and Mg = 12 and most of my plants showed Ca deficiency. After lowering Mg to 5ppm plants seem to recover.


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## Glouglou (Feb 21, 2006)

*About magnesium...*

Do I have to be concern?

Lately, it seem to be difficult to lower my KH. Normally in the 20 ppm it now stay in the 60 ppm (with RO water water change- test at 0-10ppm))

My GH is 100 ppm

If I want to calcul my magnesium using the formula :

(GH (Ca + Mg) en ppm) - (2.5 x KH (Ca) en ppm)
--------------------------
4.1
I obtain:

100 - (2.5 x 60 ppm)
----------- = 100 - 150 = -50 / 4.1 = -12.20 Mg
4.1

Maybe I need to go back to school :mmph:

How it can be a negative answer.....??????


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## Laith (Sep 4, 2004)

I don't understand this formula, especially this part:

(2.5 x KH (Ca) en ppm)  

KH has nothing to do with Ca levels but is a measure of carbonates in the water.

GH is made up (mainly) of both Ca and Mg.

The only way to figure out your level of Mg is to find a way to measure Ca. Once you have Ca and the GH, then use this formula to find your Mg:

GH = (ppm Ca/7.2) + (ppm Mg/4.4)


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## Glouglou (Feb 21, 2006)

*You right, Laith!*

(2.5 x KH (Ca) en ppm)....

(Ca) have nothing to do with the equation.

Should be:

(GH (Ca + Mg) en ppm) - (2.5 x KH en ppm)
------------------------
4.1

I find that formula that was suppose to show your Magnesium concentration only knowing your gh and kh.

I come back with you on that...

Thanks to show mwe the mistake


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## Laith (Sep 4, 2004)

I'm no chemist but I don't think any formula can show you your Mg levels with only GH and KH as the inputs.

Since KH has no relevance to Ca, Mg and therefore GH, I'm not sure how this would work. You can have a GH of 8 with an Mg level of let's say 10 and a KH of 9. You could also have a GH of 8 with an Mg level of 10 and a KH level of 12... or a KH of 5... or a KH of 15.


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## Glouglou (Feb 21, 2006)

*Humm!*

Well, I think, this formula come from the assumption that:



> Usually, in fresh water most of the cations are calcium and magnesium (In a 3:1 ratio) and most of the anions are carbonates.


coming from:http://www.thekrib.com/Plants/CO2/hardness-larryfrank.html

and this : 
Calcium and magnesium carry a positive charge and form "ion pairs" with negatively charged ions like bicarbonate, forming calcium bicarbonate and magnesium bicarbonate; Ca(HCO3)2 & Mg(HCO3)2.

and this:



> Carbonate Hardness
> 
> Carbonate, bicarbonate or temporary hardness is formed from the compounds of calcium and magnesium with carbonic acid, i.e. it is the measure of carbonate (CO3-) and bicarbonate (HCO3-) ion concentrations dissolved in the water. It is represented by the letters kH.


coming from:
http://www.sydneycichlid.com/content/?page_id=85

It seem that KH have something to do with Calcium, if it is a compound of calcium, magnesium and carbonic acid.:-s

Anyway, I will try to find where that formula come from.
In any circumstance that formula have to be a rough estimation of the real concentration...


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## Laith (Sep 4, 2004)

I think you've passed my basic levels of chemistry already!  

Anyone else have any inputs into this?


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## Glouglou (Feb 21, 2006)

*Me, a chemist, bof!*

Nope, no chemist here, input from Enstein is needed.....
Help
:retard:

Question: if that formula can or cannot give us an idea of the magnesium level???


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## Glouglou (Feb 21, 2006)

*Can it be so simple????*

I just came across another way to find Magnesium level, just knowing your GH and KH and it seem to simple to be true.


> Mg is only suplemented when Mg levels fall below 45 ppm. In this example, our GH (Total Hardness) equals 120 ppm and our KH (Carbonate Hardness) equals 80 ppm as calcium carbonate (CaCO3). Since GH equals the amount of Mg and Ca present, I can now simply subtract the KH (80 ppm) from the GH (120 ppm) and get a Mg concentration of 40 ppm


:jaw:


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## Laith (Sep 4, 2004)

The ppm measure of KH is measured as a CaCO3 *equivalent*. This in no way means that it is actually measuring CaCO3!  

If you take RO water and add sodium bicarbonate (NaHCO3), you will get a KH reading. However, that reading is not indicating the presence of Ca or Na but the presence of carbonates...


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## Glouglou (Feb 21, 2006)

*Humm!*

Laith. if I follow what you said:

Example: If I pump a lot more CO2 in my water, I add H2CO3 that will augment my KH reading and have no relation with the Ca, trowing off the Magnesium formula I present???

From the Krib (vaguely related to subject but very explicative


> H2CO3, or carbonic acid is what you get when you dissolve CO2 in
> water by the following formula:
> 
> CO2 + H2O <--> H2CO3
> ...


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