How much alkalinity will CA(OH)2 saturated vinegar add to my tank?

Miami Reef · Dec 10, 2023

A little help with the math is needed here.

260 gallon tank.

Adding 260mL of fully saturated calcium acetate. I added kalkwasser powder to a bottle of vinegar until there was noticeable precipitation on the bottom, only adding the clear solution to the tank.

How much alkalinity am I adding when I dose 260mL of the solution to my 260 gallon tank?

Thank you

Miami Reef · Dec 10, 2023

@Randy Holmes-Farley Can you help me please?

Randy Holmes-Farley · Dec 10, 2023

Yes, but it’s a bit tricky of a calculation, depending on how precise you want it.its not actually saturated calcium acetate, but saturated calcium hydroxide where the hydroxide has been messed with by the acid added.

Miami Reef · Dec 10, 2023

Randy Holmes-Farley said:
Yes, but it’s a bit tricky of a calculation, depending on how precise you want it.its not actually saturated calcium acetate, but saturated calcium hydroxide where the hydroxide has been messed with by the acid added.

Oh. Thank you for the correction. I just want a basic estimate. I’m trying to lower my alkalinity in my tank, and despite halting all alkalinity dosages, I’m finding the alk started rising.

Either it’s the calcium hydroxide, or the polyfilter I added a few days ago.

I just tested my alkalinity kit with a new standard, and it matched well, so we can rule that out.

Randy Holmes-Farley · Dec 10, 2023

I started down the road of an exact calculation, but that was taking too much effort. lol

Let's give a close approximation.

The acetic acid in vinegar (5% acidity) is 0.83 M.

Ca(OH)2 + 2 acetic acid --> Ca++ + 2 acetate + 2H2O

Ignoring anything else, that will react with half that molar amount of Ca(OH)2 to form Ca++ and acetate, so calcium is 0.41 M, and acetate is 0.83 M.

One top of that, thee is a smaller amount of Ca(OH) 2 that will just dissolve lime it normally does in water, but much less because calcium is already elevated. Let's just call that a little bit extra . lol

Thus, the solution is capable of adding 830 meq/L of alk via the acetate or is effectively 2,324 dKH and about 0.41 M Ca++ = 410 millimoles/L Ca++ = 16,400 ppm calcium.

Then add a tiny bit more, which is lost in the rounding errors.

Miami Reef · Dec 10, 2023

Randy Holmes-Farley said:
Thus, the solution is capable of adding 830 meq/L of alk via the acetate or is effectively 2,324 dKH and about 0.41 M Ca++ = 410

That’s in a 1 gallon solution??? Yep, that’s definetly the cause of the alk rising lol

Randy Holmes-Farley · Dec 10, 2023

Miami Reef said:
That’s in a 1 gallon solution??? Yep, that’s definetly the cause of the alk rising lol

That's in any volume.
If you add 1 L of 2,324 dKH to a 100 L aquarium (or 1 gallon into 100 gallons), alk will rise by 1/100th of that amount, or 23 dKH.

Of course, that's a lot of vinegar!

Miami Reef · Dec 10, 2023

Randy Holmes-Farley said:
That's in any volume.
If you add 1 L of 2,324 dKH to a 100 L aquarium (or 1 gallon into 100 gallons), alk will rise by 1/100th of that amount, or 23 dKH.

Of course, that's a lot of vinegar!

Can you help me do the math for 260mL or 0.26L of 2,324dKH in 984L?

I am genuinely not good at this type of math. I never really learned it.

Randy Holmes-Farley · Dec 10, 2023

Miami Reef said:
Can you help me do the math for 260mL or 0.26L of 2,324dKH in 984L?

I am genuinely not good at this type of math. I never really learned it.

Sure.

[0.26 L/984 L ] x 2,324 dKH = 0.6 dKH

That is significant.