Carbonic Acid is a Weak Acid

Yes, that was clear, what wasn't clear was what you do and don't know about alkalinity. So, to start I wanted to make sure we were on the same page.

I didn't exactly say a 2-part produces a "stable" equilibrium, I said that "there is actually an equilibrium system in place regardless of the dosing method."
There is an equilibrium point, either way, and this is not effected significantly by the dosing method. However, what we haven't mentioned so far is that our tanks are super-saturated with calcium carbonate. That is there is more in solution, than should be given the equilibrium of the system. The reason for this is essentially that metals, such as magnesium and phosphate, bind to calcium carbonate crystals, such as aragonite, and prevent further precipitation onto the crystals (described more here A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH by Randy Holmes-Farley - Reefkeeping.com)

The importance of this, is that keeping calcium and "alkalinity" at reef levels of suspension, given typical reef pH levels, requires significant amounts of these metas to "poison" the surface of the crystals, so that there is no available surface for them to bind. Again, this system doesn't care if you are dosing calcium reactor effluent, or 2-part, the chemistry is essentially the same.

However, if there is sufficient mg and/or P04, then within normal reef parameters, alkalinity levels, asymptotically become weighted averages of the alkalinity in the system and the alkalinity added to the system.

We can simplify this by saying X amount of 2-part will raise alkalinity Y amount per unit per unit tank volume. So, for example, B-Ionic, advertises that it will raise tank alkalinity 2.07 dkh per ml, added to 1 gallon of water.

Lets say your tank is 100 gallons and is at dkh 8 and uses 1 dkh per day. To keep up with demand, you then need to add 1 dkh per day. So, if you do the math, you would need to add about 48ml per day.

Now, again though, our system is an equilibrium system, but it is dependent on mg and also, as mentioned previously, pH. So, if we add all of this at once, our systems pH will rise quickly, forcing some calcium carbonate out of solution. This new calcium carbonate precipitate will be fresh, with no surface "poisoning" from mg et al. So, it will potentially even allow calcium carbonate to be pulled out of suspension. In extreme cases, possibly even to lower levels than before we dosed, this is referred to as a "precipitation event" and is possible due to the inherently unstable equilibrium system, that occurs in our system due to supersaturation.

A ca reactor though, for all intents and purposes, does exactly the same thing. It produces a solution, with X amount of ca and bicarbonate and adds it to the system. If you dose a specific amount of this solution, under optimal conditions, it will add a certain amount of alkalinity. On the other hand, again, if you added this solution all at once, or had low mg, you could have the same issues. The key is not the method, it is to spread out the dose, to keep up with demand and not allow "clean" seed crystals to develop. Most people find it easier to do this with a dosing pump and 2-part though, for reasons already mentioned. However, in big tanks, with lots of demand, 2-part can get expensive.

 

Wow, I attempted to read this and it went "poof" way over the top of my head

 

I did get to pretend briefly while I was reading that I was really smart.