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Old 01/18/2018, 07:03 AM   #1
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Reefiez's Avatar
Join Date: Dec 2016
Location: Hong Kong
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Randy's 2 Part DIY

I got my hands on some pharm grade calcium chloride 2 hydrate (99%-103% assay).

I am not a chemistry person, so I am looking for some input on whether my calculation or assumptions are correct.

Randy's recipe uses dowflake, which is 77-80% calcium chloride (by weight).

My first instinct is that mine is ~100%, which is ~20% purer than Randy's. So I just decrease the amount of powder to dissolve accordingly. Instead of 2.5 cups per gallon, just 2 cups.

But then I thought, I think I'm missing something, where did the 2 water molecues go?

So I googled a periodic table and searched the atomic weight of the elements, and calculate the calcium chloride portion (assuming 100% purity for simplicity).

CaCl (H2O)2 will have an atomic weight of 111.56
CaCl has an atomic weight of 75.53

Assuming 100% purity, CaCl by weight is 0.677, or 67.7%.

67.7% is about 10% LESS than Randy's Dowflake of 77-80%.

Does this mean I should add the ~10% MORE, so 2.75 cups?

I haven't touched chemistry for over a decade, am I over-thinking this? Could someone point me in the right direction?

Thanks a lot!

my reef tank is the best skimmer... of my wallet
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Old 01/18/2018, 11:07 AM   #2
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Join Date: Dec 2014
Location: Leighton Buzzard UK
Posts: 112
I started to use Rand's 2 part recipe about a 18 momths ago just bought some Calcium Chloride Dihydrate and Sodium Bicarb., I would assume as long as you can dissolve the correct amount in a gallon of RODI and I started off with 1ml per gallon of each spread over the day with a dosing pump, as long as your testing your Ca on a regular basis you can adjust if its too strong or too weak a solution

Dave 3 years still lots to learn about reefing
Mag Curve 5 Skimmer, Jebao 4 way dosing pump,4 way slave, Maxspect Gyre XF230
DSuny 2 x 40 led's
Mixed SPS & LPS

Current Tank Info: Red Sea Max C130. Self built 44x19x19 tank and stand June 2016 Maroon Clowns , 2 Firefish, 3 Pajamas, Sand sifting Goby, Engineer Goby mixture of SPS and LPS
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Old 01/18/2018, 05:26 PM   #3
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You should be very close with about 20% less. Randy's recipes are based on calcium chloride dihydrate, which I think is what you have. You might need to do some tuning.

Jonathan Bertoni
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Old 01/18/2018, 09:13 PM   #4
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Location: Hong Kong
Posts: 160
ok, i just found a huge mistake in my calculations! i missed an extra chloride lol!

seems that randy's recipe is spot on even for a 100% calcium chloride dihydrate without modification. i believe the difference would be less than 5%, which is pretty insignificant.

my mistaken calculation was that CaCl2 (H2O)2 is 147.01g/mol, with CaCl 110.98g/mol. CaCl by mass would be 110.98/147.01, coming to 75.5%, which is pretty close to Randy's 78.5%. I assume the difference is due to a little less moisture in the dowflake product. fine tuning will probably be needed.

thanks for the input dodgy67, and also bertoni for always answering so quickly!

my reef tank is the best skimmer... of my wallet
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