Kalkwasser dosing outdated or not? What would the benefits of using kalkwasser from a kalk mixer instead of dosing Ca+Alk+Mg using a modern dosing pump be?
I'd say that both are perfectly fine choices, but I've used limewater for about 15 years and I don't see any reason to change.
I like it because:
1. Since I have an ATO already, it is very little extra effort to put calcium hydroxide into it. I make up a new batch once a month or so.
2. It is inexpensive.
3. I helps boost the tank pH more than any other method.
4. It may possibly result in reduce phosphate due to precipitation of calcium phosphate.
5. A two part would require two additional pumps and timers, if I automated it.
6. Limewater may be less prone to getting skewed calcium and alkalinity. I don't measure either, and I'm comfortable that limewater keeps then in an acceptable range for my system. In fact, I know that calcium will very slowly creep up, so a I use a lowish calcium salt mix (IO) for water changes. With each batch of a two part, I'd might have to worry a bit more about exactly how well balanced the two parts were and I'd probably measure calcium and alkalinity more often.