# Please help the chemistry challenged...



## Mjproost (Nov 17, 2005)

I would like to reconstitute my Ro water using CaCl2 and MgSO4 for GH. I would like my GH to be about 5 with a 4:1 Ca/Mg ratio.

So, here's what I was thinking...

1 dGH = 17.9ppm

so..5 dGH = 89.5 ppm

So my target ppm's are 
17.9 ppm Mg
71.6 ppm Ca

so from the fertilator I would need to add the following amounts to 20 gallons of RO water to achieve the near the values I am looking for:
13.5 grams MgSO4*7H2O
15.0 grams CaCl2

Does this make sense or am I missing something?

Thanks in advance!


----------



## titan97 (Feb 14, 2005)

You numbers look fine. Just be sure to adjust to actual tank volume to reflect how much actual water you have. Be sure to subtract volume used up by the substrate, etc, and include any extra water present in any filters, etc. Also, be aware that any hydrate-d product is never an exact number. It may be more like 6.5H2O, or 7.5H2O. 

And one last thing: you'd be better off using something like RO Right or Equilibrium to reconstitute RO water. There are other minerals in the water column besides those that make up GH and KH.

-Dustin


----------



## Mjproost (Nov 17, 2005)

Well, I am actually going to add it to my reservoir. My reservoir holds almost exactly 40 gallons. So, I will double it. Also, thank you for the point about the rehydrated MgSO4. I will try it and test.



> And one last thing: you'd be better off using something like RO Right or Equilibrium to reconstitute RO water.


Well, I tried Barr's GH booster from Greg Watson and it never completely dissolved in the reservoir. It would after about 24 hours in my tank. I did not like that.



> There are other minerals in the water column besides those that make up GH and KH.


What are the other minerals that my plants and fish need that make GH? I am using Baking Soda for KH. Barr's GH booster is supposed to be be chemically similar if not identical to Equilibrium. Here's what's in it:
Potassium Sulfate - just K - I get more than enough from the KNO3 I add
Calcium Sulfate - Replaced by CaCl because it dissolves easier
Magnesium Sulfate - I am going to add this
Manganese Sulfate - Should be enough in my TMG
Iron Sulfate - Should be enough in the TMG, if not I will add Flourish Fe

I am missing something? What else is there?


----------



## Laith (Sep 4, 2004)

Mjproost said:


> ...
> 1 dGH = 17.9ppm
> 
> so..5 dGH = 89.5 ppm
> ...


Doesn't quite work like that...

17.9ppm Mg and 71.6 ppm Ca will actually give you around 14 dGH. The formula is:

dGH = (mg/l Ca/7.2) + (mg/l Mg/4.4)

For example, looking at some old calculations I've done for a 175l tank, 12g of CaCl2 adds 25mg/l of Ca. This will increase the dGH by 3.46.

Also in a 175l tank, 10g MgSO4 is 5.66mg/l of Mg which will add 1.29 dGH. The two together equals 4.75 dGH.


----------



## Salt (Apr 5, 2005)

Mjproost said:


> So, here's what I was thinking...
> 
> 1 dGH = 17.9ppm
> 
> ...


Your numbers are way off. You want a 4:1 ratio of *calcium* to *magnesium*, not *calcium chloride* to *magnesium sulfate*.

Also keep in mind the 17.85 ppm is a calcium carbonate equivalent. It assumes the only calcium containing compound in the water is calcium carbonate, so 1 dGH = 17.85 _as calcium carbonate_ which contains 7.15 ppm of calcium, and 10.70 ppm of carbonate.

Here are the correct numbers:

To increase 1 gallon of water 1 dGH using calcium chloride dihydrate (CaCl2•2H2O):

*-Add 99.239341 mg of CaCl2•2H2O per gallon of water*

To increase 1 gallon of water 1 dGH using magnesium sulfate heptahydrate (MgSO4•7H2O):

*-Add 166.379240 mg of MgSO4•7H2O per gallon of water*

To convert that to a 4:1 ratio, simply take 20% of the MgSO4 figure and 80% of the CaCl2 figure.

To increase 1 gallon of water 1 dGH using calcium chloride dihydrate (CaCl2•2H2O) *AND* magnesium sulfate heptahydrate (MgSO4•7H2O) in a 4:1 ca:mg ratio:

*-Add 79.391473 mg CaCl2•2H2O per gallon of water* (.80 dGH in 1 gallon)
*-Add 33.275849 mg MgSO4•7H2O per gallon of water* (.20 dGH in 1 gallon)

So, to apply this to your case, you want to raise 20 gallons of RO/DI water by 5 dGH in a 4:1 ca:mg ratio:

5 * 20 * 79.391473 = 7939.1473 mg = *7.94 grams CaCl2•2H2O*
5 * 20 * 33.275849 = 3327.5849 mg = *3.33 grams MgSO4•7H2O*

Keep in mind that while all this looks very precise and is based on atomic weights, there are a number of factors that can affect your actual levels and test readings in your tank when you are done. I encourage you to get a *good* test kit and take a reading after your water change. If for example your numbers are off by 15%, simply add 15% more or less of each compound next time to keep the GH stable.


----------



## Mjproost (Nov 17, 2005)

Thanks a lot for all the help. Wow, I was way off.  I don't even want to say where I got the 17.9 ppm = 1dGH. But the conversions to ppm in 20 gallons of water were from the fertilator Just one more question:



> 5 * 20 * 79.391473 = 7939.1473 mg = 7.94 grams CaCl2•2H2O /QUOTE]
> 
> How do I know that my CaCl2 is truly the "hydrated form with the "2H20"?
> I purchased mine locally from a lab supply store and the bottle just says "pure Calcium Chloride". I called the store and they didn't seem to know what I was talking about. They said "as far as I know it is pure Calcium Chloride."


----------



## Salt (Apr 5, 2005)

Since the dihydrate form tends to be the most common, that's probably what it is. As I mentioned, you can do a test after you're done and adjust accordingly.


----------



## Jason Baliban (Feb 21, 2005)

This thread just helped me leave some hair in my head ( i almost pulled it all out ). I was messing with this all day....and here is the answer.

Thanks Salt!!!

jB


----------

