Adding Calcium and Magnesium to my water

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Hi,

I'm starting EI since 2 weeks with a great succes. My concern is water. I moved recently home. I had a water of GH 10 / KH 6. In my new city, I'm at GH 14 and KH 17 :confused: So probably a lot of sodium carbonate explaining the KH>GH.

I took with me a lot of water from my old location waiting to install my own distilled water (osmosis). Now I begun mixing osmotic water with my actual GH14/KH17 tap water. I use 17% tap water and 83% osmotic to get a KH between 3-4 and a GH around 3-3.5. My tank is now at a GH of 5.5 and I expect it to be near 3 after few other water changes.

Because I have snails, shrimps and few tateurndinas, I want to increase only my GH to 6, without touching the KH. So no way to add more tap water.
- Do you think my reasoning is right on how to modify GH without moving KH?
- Is it a good idea to increase my GH or the species I talk about will accomodate to a GH of 3-3.?
- How much ppm of respectively Sulfate Calcium and Magnesium should I add to increase my GH by 3°?

Many thanks for your help
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Hi,

After some research, I found that 2.2° GH is 40 ppm
So, in my case, I should add 1:3 Ca+Mg to get a total 40ppm

On fertilator, 16g of CaSO4 and 16g of MgSO4 for a 40G (150L) volume will give me 30ppm Ca and 10ppm Mg

Is my reasoning right? And please, any other advice on my actual tap water parameters and my decision to mix it with distilled + adding Ca and Mg?

many thanks for all your support
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Hi,

Sorry to post again in less than 24h. I could afford some MgSO4 today. Can I add the Mg amount as I calculated above or am I totally wrong in my °GH to ppm conversion and estimation?

Many thanks again
 

Tom Barr

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Jan 23, 2005
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Seems about right.
MgSO4= Epsom salt, pretty cheap at most Pharmacies etc.

Regards,
Tom Barr
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Many thanks for conforting me in my calculations,
Indedd, MgSO4 is very cheap in pharmacies. CaSO4 is a bit more expensive, but nothing compared to KNO3

Regards
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Hi,

Please, what's wrong with my calculations?

I added 16g (0.1g precise balance) of MgSO4 7H2O to 90L of my water and the GH moved from 3.5 to 8?

If I trust fertilator, 16g should added about 16ppm of Mg for 90L volume, so about 1° GH maximum. How come I get those 5°GH increase?

Please help clarify this chemistry for me with directions to increase my GH by 1-2° using MgSO4 and CaSO4
 

Tom Barr

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Jan 23, 2005
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I would add about 1/4 teaspoon, 1.25mls to a 90 liter tank 2x a week.
That's plenty of Mg for the plants.
Do not worry about the "ratio", worry about limiting nutrients instead.

Regards,
Tom Barr
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Hi,

I see, this is about 2.5ppm where I added 10 looking for a +2°GH for my fish indeed

Please, if you could help me clarify my issue:

My tank is a 60G (230L) with 40G (150L) real volume measured
My tap water has a KH17 and GH 14, so unusable for my needs
I use EI with NPK and I change 24G (90L) water each week.

The water I use is a mix of 20G tap water and 4G distilled giving me a GH 3.5 and KH 4

For my fish I wanted a GH 5-6 so thought about adding MgSO4 and CaSO4, but now completely confused about the doses to increase my GH?

Many thanks for your help
 

Tom Barr

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Jan 23, 2005
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jonny_ftm;35815 said:
Hi,

Please, what's wrong with my calculations?

I added 16g (0.1g precise balance) of MgSO4 7H2O to 90L of my water and the GH moved from 3.5 to 8?

If I trust fertilator, 16g should added about 16ppm of Mg for 90L volume, so about 1° GH maximum. How come I get those 5°GH increase?

Please help clarify this chemistry for me with directions to increase my GH by 1-2° using MgSO4 and CaSO4

I do not use a fertililator or a calculator.
I take the weight/volume and the molar mass for the calculation.

This gives me ppm's of Mg.

Similar for the CaCl2 or CaSO4.

There's some water added for all these, so there might be some variation, but should not be that much.

Also, did you make a reference solution for the GH test kit?
If not, you might be worrying based on a bad test kit reading.

As long as you know what substance you have, then the ppm's should be fine.


Regards,
Tom Barr
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Hi and thank you for helping me in this thread,

No, I didn't use a reference GH solution, but used two different kits, JBL and Tetra, both same reading

Maybe I'll have to dose my MgSO4 and CaSO4 powders until I get the °GH I need simply. Seems in my case, this ppm to GH conversion isn't working as supposed :confused:

Anyhow, for a situation like mine, tap water of GH 14 and KH 17, how you would proceed to get a final solution with a KH3 and GH near 6? It's getting complicated with this tap water because I'm not used to such high KH levels

Many thanks for the support
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Edit: check later post, this calculation showed to be wrong too

Hi,

I solved the mystery, all is in chemistry/definitions.

GH is the German version of TH (French definition)

1° TH corresponds to 10 exp-4 mol/L that is 4 mg of calcium or 2.4 mg of magnesium per liter (ppm)

1°TH = GH/0.56 so 1°GH = 0.56*TH

1°GH --> 2.24 ppm Ca or 1.344 ppm Mg

So it is not the same ppm defintion of GH it seems and I was adding too much Magnesium, that's why my GH was climbing so high

Hope it would help people better adjust their GH when supplying Mg and Ca salts
 

Tom Barr

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Jan 23, 2005
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16 grams of Epsom salt?

That's a lot.

Try 1/4 teaspoon 2x a week.
That should be fine to meet demand for Mg.

Regards,
Tom Barr
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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I'll do,

I wanted it too maths and ppm precision, but I completely missed it. I really added too much Mg in my 60G tank (only 40G water) but the fish seems fine hopefully

I'll add what you propose, 2x1/4 tsp is for a 40-60G tank?
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Hi,

As I just got the CaSO4, I tested and my above calculations showed to be wrong and giving a low GH increase

So, I used Seachem Equilibrium instructions and adapted the doses of CaSO4 and MgSO4 for my volume with fertilator

This, theorically gives:

In Fertilator: 16g Seachem Equilibrium in 80L water ---> 16.12 ppm Ca and4.82ppm Mg
That's also +3°GH if I believe Seachem instructions

I tested in my 90L water preparation (74L distilled+ 16L tap ---> GH 3.5°). With Fertilator help, I added 5.3g CaSO4(2H2O)=16.26ppm Ca and 4.5g MgSO4(7H2O)=4.93ppm MgSO4 (7H2O)

After adding the MgSO4, GH moved from 3.5° to 4.5°
After adding the CaSO4, GH became 6.5°

So, for people that have a +/-0.1g balance like me (or even a +/- 1g):
- Fertilator can be used to dose Mg and Ca in ppm
- 16.12 ppm Ca ----> +2°GH
- 4.82 ppm Mg ----> +1°GH

Now, if some one can give the math behind this ppm to °GH conversions, it would be great
 

incubus3x3x3

Junior Poster
Nov 7, 2008
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Europe - Romania - Constanta
The simplest way is to calculate in moles and then turn back to mass.

1dGh = 10mg/l CaO (this is the deffinition)
molar mass of Ca is 40 and O is 16 (aprox.) so the molar mass of CaO is 40+16=56 g/mole

so 1dGh = 10mg/l of CaO => 1dGh=10/56 mg/l*mmole/mg => 1dGh = 0.1786 mmoles/l of CaO

Turning to Ca, in moles, that means 1dGh = 0.1786 mmoles/l of Ca (or Mg). We measure in moles so no mass conversion is necessary here.
Let's go back to mass:

1dGh = 0.1786 mmoles/l * 40 mg/mmoles of Ca => 1dGh = 7.1429 mg/l of Ca

Simillar for Mg, we can do the same, but the molar mass of Mg is 24 g/mole

1dGh = 0.1786 mmoles/l * 24 mg/mmoles of Mg => 1dGh = 4.286 mg/l of Mg

In conclusion:
aprox 7.143ppm of Ca = +1dGh
aprox 4.29ppm of Mg = +1dGh

Your measurement was pretty close.

All the best.
Andrei.
 

jonny_ftm

Guru Class Expert
Mar 5, 2009
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Many many thanks for the math. I found nothing about the definition of GH like you state in mg/L of CO despite many research, so I couldn't solve it in anyway

Now, with the clear definition you brought, it is easier to calculate. I'm happy also that you could confirm that my practical measurements were so close to the theorical calculations up to +/- 1ppm. The deviation was due to the precision of GH kits to 0.5 °GH and to the precision of my balance (+/- 0.1g) and also maybe impurities in CaSO4 hydrated. I could get a better precision, but it would cost me a lot of GH reactive drops for my tries.

I'll save this info and adapt my calculations based on your math.

many thanks again