CO2 and the interaction with Kalkwasser and CO2 scrubbers

[re76]

Is it possible to have too little CO2 in our water?

I am currently running a CO2 Scrubber on the air intake of my skimmer controlled by a 3-way solenoid valve for when my PH drops below 8, along with kalkwasser, and dosing 2 part.

I feel like my tank is not stocked enough to justify 2-part and kalkwasser. But I am still needing both of them to maintain my alk, which I test daily.

I am wondering if there is something else going on that is making my Ca and Alkalinity dosing inefficient.

My hunch is that with Kalkwasser AND the CO2 scrubber, there is not enough CO2 in the water, and so my Kalk is not increasing Alk as much is it should. OR that the same sort of thing is happening with my 2-part Alk solution (Sodium Carbonate, which also needs CO2).

I am considering one of the following changes:

• Switch to a Sodium Bicarbonate solution for 2 part
• Switch off CO2 Scrubber
• Stop dosing Kalk

Chemically speaking is this even possible? Could too little CO2 in the water cause common balanced dosing methods to be less efficient?

 

[Randy Holmes-Farley]

Is it possible to have too little CO2 in our water?

I am currently running a CO2 Scrubber on the air intake of my skimmer controlled by a 3-way solenoid valve for when my PH drops below 8, along with kalkwasser, and dosing 2 part.

I feel like my tank is not stocked enough to justify 2-part and kalkwasser. But I am still needing both of them to maintain my alk, which I test daily.

I am wondering if there is something else going on that is making my Ca and Alkalinity dosing inefficient.

My hunch is that with Kalkwasser AND the CO2 scrubber, there is not enough CO2 in the water, and so my Kalk is not increasing Alk as much is it should. OR that the same sort of thing is happening with my 2-part Alk solution (Sodium Carbonate, which also needs CO2).

I am considering one of the following changes:

• Switch to a Sodium Bicarbonate solution for 2 part
• Switch off CO2 Scrubber
• Stop dosing Kalk

Chemically speaking is this even possible? Could too little CO2 in the water cause common balanced dosing methods to be less efficient?

CO2 can be too low because it makes the pH too high. It is never too low, however, to have limewater provide alkalinity.

If pH is not too high (say, above pH 8.6), there is plenty of CO2.

 

[re76]

CO2 can be too low because it makes the pH too high. It is never too low, however, to have limewater provide alkalinity.

If pH is not too high (say, above pH 8.6), there is plenty of CO2.

Alright. Thanks for the response Randy! Makes me feel better, but still confused how I am consuming so much Alkalinity and Calcium. Back to the drawing board.

 

[Randy Holmes-Farley]

Have you determined your dose per day in dKH?

 

[re76]

No, but I take really detailed notes so let me take a stab at calculating that.

Using a system volume of 105 gallons, I am dosing about 72 mL of 2-part a day. I use 2 standard measuring cups of sodium carbonate dissolved in 1 gallon of water. Based off the Bulk Reef Supply calculator for 105g a 75mL dose will raise my dKH by about 1 dKH. So that is the 2-part contribution.

For Kalk I am using a Avast Marine kalk stirrer which is fed by a peristaltic pump which runs for 7 minutes every 30 minutes, or 14 minutes every hour. That is 336 minutes per day. I have measured the peristaltic pump rate at around 11 mL per minute so that means I am dosing about 3696 mL of saturated kalk a day. Using the assumption that kalk is about 45 times less powerful than 2 part, that comes out to be roughly equivalent to 82 mL of 2 part per day or 1.1 dKH.

So there was a lot of back of the napkin math going on, but I would estimate I am dosing about 2.1 dKH per day. Which seems crazy, where could I be losing that much dKH? My tank is still relatively new and is just now starting to get some corraline algae taking hold.