How much saturated kalkwasser would it take to raise a net 10 gallon system from pH 8.2 to 8.3?

[powers2001]

How much saturated kalkwasser would it take to raise a net 10 gallon system from pH 8.2 to 8.3? I'm thinking of building a kalk dripper and need to estimate how much volume of container for the liquid.

 

[Randy Holmes-Farley]

Just to clarify, limewater (kalkwasser) is an alkalinity additive, and should be dosed based on the alkalinity demand of the tank, or else the alk will likely get too high.

To answer specifically, the impact on pH will depend inversely on the alkalinity in the tank, so the effect at 6 dKH is twice that at 12 dKH. The effect is also larger with lower starting pH.

In my experiments, adding 0.5 meq/L (1.4 dKH) of hydroxide (equivalent to 1.25% of the tank volume of saturated limewater) boosted the pH of new IO salt mix (alk about 11 dKH) by about 0.66 pH units (pH 8.1 to 8.76).

So I'd estimate that it will take about 0.2% of the tank volume, or 0.02 gallons (75 mL).

The pH rise is instantaneous, then declines over time as CO2 enters the water.

 

[powers2001]

Okay for the first time I try the dripper I won't dose over 75mL slowly. How much Calcium Hydroxide would I need for that much water to make the solution saturated. I don't want the slurry at the bottom of the container to get dripped.

 

[Randy Holmes-Farley]

Okay for the first time I try the dripper I won't dose over 75mL slowly. How much Calcium Hydroxide would I need for that much water to make the solution saturated. I don't want the slurry at the bottom of the container to get dripped.

Not much.

About 0.11 grams.

2 teaspoons per gallon is about saturation.

 

[powers2001]

So about 1/4 teaspoon for 75 mL?

 

[JimWelsh]

So about 1/4 teaspoon for 75 mL?

There are 3785 mL in one gallon, so 75 mL is 75/3785 = about 0.02 gallons times 2 tsp. = 0.04 tsp., which is 1/25 tsp for only 75 mL. Better to mix up a larger batch with excess calcium hydroxide, let it settle, and just take 75 mL of the supernatant (clear liquid on top), than to try to measure an amount that small.