Question on vinegar and kalk

ReefBeta

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Tradition wisdom said adding 45ml vinegar to 1 gallon of water can increase kalk dissolved from 2 tsp to 3 tsp. My question is, if we add more vinegar, will it be able to dissolve more kalk, like 90ml per gallon for 4 tsp or 135ml per gallon for 5 tsp?
 
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Randy Holmes-Farley

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You can dissolve more, but the drawbacks to adding so much vinegar become significant.

When I was manually dosing vinegar, I took the approach of saturating the straight vinegar with calcium hydroxide and dosing that clear fluid, avoiding any pH drop from the vinegar. But that approach adds lots of vinegar and not that much calcium and alkalinity.

Here's the original rationale for the 45 mL/2 tsp from 22 years ago:

 
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You can dissolve more, but the drawbacks to adding so much vinegar become significant.

When I was manually dosing vinegar, I took the approach of saturating the straight vinegar with calcium hydroxide and dosing that clear fluid, avoiding any pH drop from the vinegar. But that approach adds lots of vinegar and not that much calcium and alkalinity.

Here's the original rationale for the 45 mL/2 tsp from 22 years ago:


I can dissolve 2 teaspoons of kalk into 200ml straight vinegar completely, that's almost 20 times the strength of saturated kalk in just water. That's quite a lot of calcium and alklinity isn't it? The third teaspoon didn't dissolve completely, but I'm not sure how much of it was not dissolve. What's the theoretical saturation of kalk in straight vinegar?

Is the amount of vinegar linear to the additional kalk the solution can dissolve? How does the dissolve graph go from 2 teaspooons per gallon with 0% vinegar, to 2 teapsoons per 200ml with 100% vinegar or more.
 

Randy Holmes-Farley

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I can dissolve 2 teaspoons of kalk into 200ml straight vinegar completely, that's almost 20 times the strength of saturated kalk in just water. That's quite a lot of calcium and alklinity isn't it? The third teaspoon didn't dissolve completely, but I'm not sure how much of it was not dissolve. What's the theoretical saturation of kalk in straight vinegar?

Is the amount of vinegar linear to the additional kalk the solution can dissolve? How does the dissolve graph go from 2 teaspooons per gallon with 0% vinegar, to 2 teapsoons per 200ml with 100% vinegar or more.

200 mL is a lot of vinegar to dose in a day.

Normal 5% acidity vinegar contains 50 grams of acetic acid per liter, for an acid concentration of 0.83 M.

That will allow the dissolution of half that number of moles of calcium hydroxide (since it has 2 OH- per mole).

So the vinegar allows dissolution of 0.41 M calcium hydroxide.

Normal dissolution of calcium hydroxide in pure water is 0.0204 moles/L.

Thus dissolving calcium hydroxide in straight 5% acidity vinegar makes it about 0.41/0.0204 = 20x as concentrated as normal limewater (kalkwasser).

Yes, it is approximately linear with lower amounts of vinegar mixed with water.
 
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200 mL is a lot of vinegar to dose in a day.

Normal 5% acidity vinegar contains 50 grams of acetic acid per liter, for an acid concentration of 0.83 M.

That will allow the dissolution of half that number of moles of calcium hydroxide (since it has 2 OH- per mole).

So the vinegar allows dissolution of 0.41 M calcium hydroxide.

Normal dissolution of calcium hydroxide in pure water is 0.0204 moles/L.

Thus dissolving calcium hydroxide in straight 5% acidity vinegar makes it about 0.41/0.0204 = 20x as concentrated as normal limewater (kalkwasser).

Yes, it is approximately linear with lower amounts of vinegar mixed with water.
So if using calcium carbonate (like from calcium reactor media) instead of calcium hydroxide, is the max dissolution of alkalinity the same?
 
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Randy Holmes-Farley

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So if using calcium carbonate (like from calcium reactor media) instead of calcium hydroxide, is the max dissolution of alkalinity the same?

No, it requires much lower pH to dissolve, so somewhat less will dissolve, and it will bubble and foam.

i discuss using calcium carbonate in various ways here:

 

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I would like to piggyback on this thread but ask a little different question. I recently started daily manual dosing of NoPox. I also dose kalk via a stirrer and dose hourly from 7 pm – 12 pm and run a Ca reactor 24/7. Before I started carbon dosing, even with my calcium reactor running my pH was getting above 8.4 in the late afternoon, which is why I switched from dosing kalk 24/7 to my current 7:00 PM to 12:00 PM schedule. Now that I’ve started carbon dosing, my morning pH drops below 8, and my pH struggles to hit 8.2 in the late afternoon. I realize this isn’t a big issue, but I would like to hit 8.3 pH late afternoon if there is a simple way to do it. My thought was to add a little pickling lime directly to the flask I store and dose the NoPox out of. I shake before using every time anyway so even if a little dropped out of solution, I figure the shaking would help to get back into solution. That said, I don’t know if adding a little pickling lime to the flask would even help achieve my desired results. Before playing around with my kalk dosing schedule, which might also work, I wanted to find out if something like this might work.
 

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  • Alkalinity (most)

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  • Magnesium (most)

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