Dosing Supersaturated Kalkwasser

[iTread]

My tank is finally taking off and I have gone from 18 ml/day of kalk to about 900 ml/day in about 3 weeks. I am dosing super saturated kalkwasser (3 tsp of mrs wages, 45 ml of vinegar in 1 gallon rodi). I mix about 2 gallons at a time (2, 1 gallon jugs). After a day or two the bottom of the 1 gallon mixed container is white. The question I have is: does that mean that my clear solution is no longer super saturated? Or is that just the normal precipitate as I would find with a normal saturated solution? and I am still dosing the same super saturated solution even after 2 or 3 days?

 

[Randy Holmes-Farley]

To clarify, the solution is never actually "supersaturated", but I agree it certainly dissolves more than without the vinegar.

Just like normal limewater, reaction with carbon dioxide will produce some calcium carbonate, and if the solution started clear and then got some solids, that is the likely explanation. it does lower potency somewhat.

Unless you are evaporation limited, I personally do not prefer to mix vinegar into the limewater, and when I used both (vinegar and limewater), I dosed them independently to get better control of them,.

 

[iTread]

Ok...so, the vinegar just helps the solution become fully saturated (not necessarily more concentrated/super saturated)? I guess the reason I went the vinegar route was mainly to be sure that the solution was the maximum potency and, I thought, more likely to be a more stable concentration. Therefore, all I would ever have to do would be to adjust the amount of Kalk as my tank's needs grew. I also dosed vodka before, but as my kalk/vinegar grew it seemed excessive to do both.

 

[Randy Holmes-Farley]

Ok...so, the vinegar just helps the solution become fully saturated (not necessarily more concentrated/super saturated)? I guess the reason I went the vinegar route was mainly to be sure that the solution was the maximum potency and, I thought, more likely to be a more stable concentration. Therefore, all I would ever have to do would be to adjust the amount of Kalk as my tank's needs grew. I also dosed vodka before, but as my kalk/vinegar grew it seemed excessive to do both.

It is more concentrated, but is not more likely to be stable if you use the ratio you used. If you use so much vinegar that the pH is low (4-10) and the solution is not even saturated with respect to calcium hydroxide, the risk is bacterial growth, although it will be chemically stable to precipitation.

 

[iTread]

Ok...is there a vinegar - kalk ratio that maximizes the saturation, but is also more stable? I don't mind the bacterial growth as that is added bonus since I was already dosing vodka to reduce total nitrates .

 

[Randy Holmes-Farley]

Ok...is there a vinegar - kalk ratio that maximizes the saturation, but is also more stable? I don't mind the bacterial growth as that is added bonus since I was already dosing vodka to reduce total nitrates .

More stable toward precipitation would mean it has a much lower pH, where CO2 entering does not form carbonate. Unfortunately, at that low of pH (say, below 9) bacteria will thrive and consume the acetate. I don't think there's a good way around that, unless you make the solution so concentrated that bacteria cannot live due to the ionic strength. That concentrated might be OK in a dosing pump, but not an ATO.

When I manually dosed vinegar before getting a dosing pump, I added enough calcium hydroxide to full strength vinegar to allow there to be no pH drop when adding the vinegar. That solution still has a very high pH, above 11.

 

[iTread]

The end of this month long saga is that I am now dowing 1700 ml to maintain 8.1 Alk and 410 Ca and 1300 Mg. pH fluctuates between 7.9 to 8.1 still. I did have a follow up question on the Vinegar. Does mixing vinegar with Kalk reduce the ammount of carbon available for bacteria (nitrate/phosphate export)? Ie, if I am mixing 45 ml of vinegar in 1 gallon and I use that in about 2 days, am I effectively dosing 45 ml of vinegar, or is it less due to the reaction with the Kalk?