Reef Chemistry Question of the Day #108 Two Part Recipe

Randy Holmes-Farley

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Reef Chemistry Question of the Day #108


In a balanced two-part calcium and alkalinity recipe, including my DIY recipe, why is it necessary to use two parts instead of combining them into a single additive?


A. Calcium carbonate will precipitate and will not redissolve in the aquarium
B. Calcium sulfate will precipitate and will not redissolve in the aquarium
C. You can mix them; I do it all the time
D. Magnesium sulfate will precipitate and will not redissolve in the aquarium

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redfishbluefish

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A......Na2CO3(aq) + CaCl2(aq) --> 2NaCl(aq) + CaCO3(s)


I pulled a Homer "Doh" and did "C" when I mistakenly topped off my Calc dosing container with Alk solution.....saw it first hand. They are now very clearly labeled.
 
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beaslbob

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the calcium and alk parts when combined will produce calcium carbonate which will not redisolve.
A.
I got really really smart one time and added the 300ml of the magnesium to my calcium additive. Went happily along until I shook the bottle and found a bit white clump there. :bigsmile:
Calcium sulfate I believe but that was combining the calcium and magnesium parts not the calcium and alk parts?
I kinda knew this so the answer is not C. :xd:
 

JimWelsh

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Well, since one part is sodium *carbonate* and the other part is calcium *chloride*, and there is no sulfate anywhere in sight, that rules out answers B and D. Just like redfishbluefish, I, too have "pulled a Homer" before. Answer is A.
 
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Randy Holmes-Farley

Randy Holmes-Farley

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the calcium and alk parts when combined will produce calcium carbonate which will not redisolve.
A.
I got really really smart one time and added the 300ml of the magnesium to my calcium additive. Went happily along until I shook the bottle and found a bit white clump there. :bigsmile:
Calcium sulfate I believe but that was combining the calcium and magnesium parts not the calcium and alk parts?
I kinda knew this so the answer is not C. :xd:

Yes, that precipitate you saw was likely calcium sulfate.

Right, NOT C. :D
 

beaslbob

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Is it possible the industry lobbists for the 1 gallon jar industry just lobbied to sell more jars?
 
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Randy Holmes-Farley

Randy Holmes-Farley

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And the answer is...A. Calcium carbonate will precipitate and will not redissolve in the aquarium

The high calcium and carbonate will result in almost instant precipitation that cannot redissolve in aquarium water.

Answer B is a bit of a trick:

B. Calcium sulfate will precipitate and will not redissolve in the aquarium

Calcium sulfate will definitely precipitate if you mix the two parts of a two part system together, but calcium sulfate will redissolve in the aquarium.

Magnesium sulfate is very soluble. It is interesting (to a chemist anyway) that despite the fact that calcium and magnesium are so similar, the magnesium sulfate is very soluble while calcium sulfate is much less so. I believe that relates to the size of the calcium and magnesium ions, and how they fit into a crystal with sulfate.


 

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