Quantrill said:

molecular weight of SO4 is 96.06
S= 32.06
O=16 theres four of them so 64
32.06+ 64= 96.06


32.06/96.06= 33% So sulfate is 33% sulfur.

if there is 246ppm sulfate and you want to know the sulfur ppm:

246*33%=81

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So to put it all together, what's the molecular weight and ppm of MgSO4? Is this in ppm = EC x 500?

ttystikk, I think you only need to know the ppm conversion factor when you're talking about a commonly used ppm meter reading. We're calculating the hard ppm of elements in solution, there isn't really a correlation between the numbers we figure out and a ppm meter reading. For example, you can't come up with a profile of 150N, 50P, 200K etc., calculate the ppms of all elements, mix up the salts in a solution and say "well then my hanna meter should read whatever all those ppms add up to.". As you might already know the common ppm meters are only EC meters that use one of a couple conversion factors(sodium or NaCl and others) to display ppm and since different elements and molecules contribute differently to the overall EC, theres no real way to accurately convert between the two that I know of. There may be some crazy math you could do, but I don't know anything about it.

The molar mass of MgSO4 is about 120u (all and the elemental percentage breakdown is Mg=20.1922%, S=26.6395%, O=53.1683%. You really need to know the mass (weight) of MgSO4 and the exact volume of water you're going to dissolve it in to figure out ppm. If you put one gram of MgSO4 in one liter of water you will have 201.922ppm of Mg, 266.395ppm of S and 531.683ppm of O. Remember ppm in water is the same as mg/L. Also to tie in the above, if you did put one gram of MgSO4 in a liter of water your Hanna meter would not read 1000ppm but you would still have the listed elemental ppms in solution. And not to jumble things up too bad, maybe someone else can help clarify, but I think when you mix MgSO4 in water it picks up 7 H2O molecules to become the hydrate form of the salt. What I'm not sure about is whether or not to include those extra H and O atoms into the calculations or not and also if all salts have something like that when dissolved. I just assume that most other salts simply break into their respective elements upon solution. If someone could help clear that up or offer an other input I'd appreciate it.

Also if there's any chemists out there, I'm have a little trouble with some defintions. It seems like the term atomic mass takes into consideration different isotopes of elements and is a very exact, sample by sample measurement of something. Atomic weight on the other hand seems to be more of a "most commonly found" number and includes an average of most common isotopes. Do I have that right and is it important to keep them straight or are they used interchangably (even though they're not interchangable)? Also are g/mol and daltons(atomic mass units) somehow interchangable? When I was figuring out what I thought was the molecular mass of MgSO4, I found the atomic weights of the individual elements and did the math and it came out to about 120u. Then I checked on an online calculator and it gave me 120 g/mol, how are these two units related or what am I not understanding about their relationship?

^^^ great post HG23.

I second Cap's motion, very informative.

It is essential to know that sticking an EC meter (that's what all ppm meters are) into water only picks up that solution's EC, or Electrical Conductivity. Not all materials in solution will affect EC the same, or at all.

It is good to know that when I put some epsom salts in my res, my ratio is 10 parts Mg to 11 parts S, and that was my original question, poorly worded as it was.

I'm gonna shill for a pet cause though, and advocate that everyone use EC instead of ppm, because commonly used ppm scales do have different conversion values (EC x500, or x 700, or x 740, to name a few), where EC is the actual measurement. Less chance for confusion.

Capulator said:

^^^ great post HG23.

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perfect

Yeah I wish I had read that post when I was trying to figure out how many ppms of Ca I was adding when I used CaCl2. Ended up emailing fatman on ebay. LOL. Cool of him to give me the lowdown, but not in such a simplistic way as HG23 managed to do just now.

ttystikk said:

So to put it all together, what's the molecular weight and ppm of MgSO4? Is this in ppm = EC x 500?

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Epsom salt is magnesium sulfate heptahydrate. Even though it is considered a dry salt, it actaully has seven waters of hydration and a formula of MgSO4·7H2O. So you have to include the seven molecules of water in the calculation to determine the percentage of each elemet in the compound.



http://www.lenntech.com/calculators/molecular/molecular-weight-calculator.htm

to figure ppm per liter of total solution you simply multiple the percentage of the element in question by 10, for example:
9.86%Mg x 10= 98.6ppm Mg from one gram of epsom in one liter of total solution.

to figure ppm per gallon of total solution you simply multiply the percentage of the element in question by 2.64, for example:
9.86%Mg x 2.64=26ppm Mg Mg from one gram of epsom in one gallon of total solution.


To calculate an estimated EC you can use the limiting molar conductivity factors as explained in this paper: http://www.currentseparations.com/issues/18-3/cs18-3c.pdf , this is the method HYDROBUDDY uses. However it is just an approximation as there are too many variables involved for accurate calculations.

*sharpening my pencil* cuz I got homework to do!

I don't understand the 2.64 conversion to gallons- aren't there 3.76 liters per gallon, or am I missing something here? EDIT; Nevermind, I missed that first conversion to g/liter. 26ppm @ 1g/gal is 1/3.76 of 98ppm @1g/liter. Homie slow sometimes, but I gets it eventually...

This tells me that adding only .5 grams of epsom salts per gallon is too low to do any good, I gotta boost it up.

Thanks again Quantrill, this is quite the education you're providing here!

Great post, but for people who want an easier way: (btw i have posted this a few times....)

Epsom salt, magnesium sulfate, Mgso4:

Mg: 9.8%
S: 13%

or

1g Epsom salt =

Mg: 98 mg/l or 98 ppm
S: 130 mg/l or 130 ppm

or

1g/10 liters =

Mg: 9.8 ppm
S: 13 ppm

or

1g/gal=

Mg: 26 ppm
S: 34 ppm

BUMP.

Still rockin' the jack's over here. Though now I'm at .8 EC of the whole solution and 2EC of sea salt. Been working wonders.

organicness said:

Still rockin' the jack's over here. Though now I'm at .8 EC of the whole solution and 2EC of sea salt. Been working wonders.

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so total 2.8 EC? Can you link the sea salt? sounds interesting.

I use Real Salt brand from the store. The pink stuff from Utah.

http://www.realsalt.com/

And eventually I'll use Sea90 instead, this stuff is just here close by. Sea90 is a way better buy though.

I'm gonna run my Jacks until I've finished, then get some basic salts and do the six-pack. I still need to figure out how to read the ratios and then figure out how to mix the salts to get what I want...

organicness said:

I use Real Salt brand from the store. The pink stuff from Utah.

http://www.realsalt.com/

And eventually I'll use Sea90 instead, this stuff is just here close by. Sea90 is a way better buy though.

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straight salt from the grocery store!!!??? You surprised me. :eek:. I was not expecting that.

ttystikk said:

I'm gonna run my Jacks until I've finished, then get some basic salts and do the six-pack. I still need to figure out how to read the ratios and then figure out how to mix the salts to get what I want...

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Do you know how to use hydro buddy or the nute calculator from canna stats?

Capulator said:

straight salt from the grocery store!!!??? You surprised me. :eek:. I was not expecting that.

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Sea salt, yes. Not regular table salt. Sea salt has 80+ balanced minerals in ionic form. Table salt does not, and the sodium in the table will absolutely kill the plants. But... having the rest of the minerals in abundance alongside sodium with the sea salt, you get no dying plants. :)

Dr Murray had stated in one of his publications that the ocean contains no terminal disease. It's the perfect balance of minerals to play host to so many different kinds of life. It also helps to improve resin production because resin is, after all, made of rare earth minerals.

ordered some sea 90 today to try.

Nice. Keep me posted on it, it's been a wonderful thing for me. It doesn't take much at all to bring the EC up.

organicness said:

Nice. Keep me posted on it, it's been a wonderful thing for me. It doesn't take much at all to bring the EC up.

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Of this, at least, I have no doubt. I know what all is in sea salt- I use it myself, on my food- but much of the content is still sodium chloride and those aren't minerals plants want or need in any concentration. Surely there are better ways to get available micronutrients?

Have you read this info?



And also his book, Sea Energy Agriculture

There's so much work behind the use of sea solids in agriculture and it's been kept a secret for so long. Well, not purposely kept a secret, I don't think, but the big ag companies want farmers to only think that 16 elements are essential for thriving plants. Not the case.

And yes, a bunch of the content is still sodium chloride, but it's a similar argument to Marinol. With focusing on just one of the constituents of the whole, the product doesn't work like it would with the rest of the elements in symbiosis. Give it a test on a plant or two in soil(less). I just water in my hydro nutrients for my plants in promix, still with sea solids and all. Im sure you'll love it.