I haven’t been able to figure out how to calculate ppm when i find a recipe I’m interested in brewing. I usually use distilled water and I like to build my water profile from that when brewing all grain. How would I, for example, calculate 75 ppm of Ca in 7 gallons of distilled water?
Welcome! Well, that’s a huge rabbit hole to go down ifn yer doing it long hand… there are water calculators online that’ll do the work for you…. See, I couldn’t get my pc to talk with those programs, so I followed Palmers “ how to brew” book. Formulas are in there…
Brun’water is a great online one… the author of it used to show up here once in a while.
Tell us about what you brew and such… many great peeps here that are full of knowledge!
Sneezles61
I am a MS chemical engineer with a good knowledge of water chemistry (master in environmental engineering with several water chemistry courses). Even I use the programs as they are easy to use. Here is a link to one
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Hey MikeM, when the equation is 50 ppm in a 5 gallon volume… was I understanding that’s 50 ppm to each liter? Not the whole 5 gallons?
Sneezles61
This can be calculated by hand. It’s just a whole lot of work. Better to use a tool like mentioned above, or an Excel spreadsheet. But for anyone interested, I can walk you through the thinking process.
First you need to know that ppm is mg/liter. So for example if there’s 1000 mg in a gram, and 1000 grams of water in a liter, then a liter of water has 1 million mg, which is where the parts per million term comes from.
But we’re not talking about water. We’re talking about calcium… and more specifically, calcium salts, usually calcium chloride (CaCl2) or gypsum (calcium sulfate, CaSO4). But if you add 1 mg CaCl2 or 1 mg gypsum to a liter of water, it’s not all calcium, a good part of it is chloride or sulfate. So… now what? Well, ever heard of a periodic table? Yeah…
From a periodic table, you’ll see that Ca has a molecular weight of 40.078, Cl = 35.453, S = 32.065, O = 15.9994.
Oh great. Well what does that tell us? It tells us that out of all the calcium chloride, which has one calcium and two chlorine atoms, you’ve got the calcium being 40.078 out of the whole thing of (40.078 + 35.453 + 35.453). Dividing that out, we find out that calcium chloride is 36.1% calcium by weight, or 1 gram contains 0.361 grams calcium and 0.639 g chloride.
Ugh… this is a lot of math, isn’t it!? But we can still figure this out. So… if I want 75 ppm calcium, that’s 75 mg/liter. To get there, I know we’ll need more than 75 mg calcium chloride (if we use that and no gypsum) because a lot of it is chloride. How much? Well, divide the 75 by 0.361 = 207.75 mg, which is 0.20775 grams, per liter.
How many liters do we have? Well the OP said 7 gallons. Now you need to know that there are 3.79 liters in a gallon. So multiplying, we have 26.5 liters.
Finally, multiplying again, 26.5 L * 0.20775 g = 5.5 g CaCl2. Sounds about right. Passes the giggle test.
Salts like these are usually measured in grams because ounces are 28 times bigger so the amount of ounces would be tiny, 0.1944 oz. That’s probably more difficult to measure unless your scale measures ounces with that precision. And it’s an extra math step that isn’t needed for most scales. Just weigh it in grams and be done.
I haven’t done all the math for gypsum (CaSO4) because… I don’t feel like it. But you’ll get something in a similar ballpark of a few grams in 7 gallons or 26.5 liters.
Hope this is helpful to anyone curious who might want to learn to do this stuff when software isn’t handy. I love math enough that I just do this kind of stuff for fun once in a while. But I’m too tired to do it twice tonight.
Cheers all.
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Thank you!
And other parts is how to measure by weight, the volume needed…. I used a digital kitchen scale… switched to metric and usually used a small amount of distilled/RO water that I’d add the precise amount… well, only as accurate as the equipment I have.
Sneezles61
Bravo Dave. I’m impressed you know that since I kinda glazed over about the periodic table part 
Guess I’m stuck with online calculators.
Wow, thanks for breaking all of that down for me and taking the time! It is definitely appreciated!
Sneezles-50 ppm is a concentration not a weight. ppm=mg/liter and 1000 ppm is 0.1 wt percent. So concentration is independent of volume. To get the weight of salt required you need to multiply concentration by volume with appropriate conversion factors.
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Yup, I was aware…
Sneezles61
@dmtaylo2 very impressive Dave. I will stick to online Bru’n water since that made my head hurt. 
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