What I meant was that at higher ambient CO2, more kalkwasser can be added without the pH getting as high, so the alk can rise higher.
For example, with enough CO2 in the air, you might never even get to pH 8.2 (lots of folks are in this situation), and alk might get quite high if demand is not consuming it.
Don't be misled by examples where people have so much alk demand that they even use other addition methods asc well.
The idea that one can add large amounts of kalkwasser without alk getting excessively high only applies in specific scenarios. It is not a general principle, and many folks misunderstand this.
I can attest to this. If you pH set point is set for 8.4 and you have a a lot of atmospheric CO2 in the air, you have to fight to keep it at that level. Thus the Alkalinity raises to the equilibrium in your home.
Here is a 24 hour snap shot of my home's CO2 levels. I opened up all the windows in my living room. Notice the huge drop in CO2 levels.
On my Apex, I use the Neptune DOS to dose in saturated kalkwasser from a bucket. My Neptune DOS will dose up to 3000 mL of saturated kalkwasser per 24 hours. My set point written into the DOS settings is 8.2 (through trial and error I found this to be best for me). This is largely dependent on photosynthesis in the tank and atmospheric CO2. Typically the amount dosed into the system is only maximum of 1500 mL. The point of setting it higher (3000 mL) is the DOS sets the interval and amount. I found this value to work best for me.
This is my pH in a 24 hour period. My lights turn off at 7 PM and turn on at 6:30 AM, which you can see how the pH drops ever so slightly at night.
The issue with doing alkalinity this way is that people will notice rising alkalinity as the DOS programming fights the atmospheric CO2. So one has to really find the balance of what your atmospheric conditions and tank conditions that are in the home.
Over all I really like this method as its very inexpensive. Once you find out the settings you are rocking and rolling. Alkalinity has been really stable for me. I test about once a week. Corals are happy and growing. Not out of control but growing.
I would consider a balling method in the future to better address trace element balance and magnesium, but for now this works fine. Especially on a budget.