So, if I mix my kalk in a jug, let it sit a while (capped) and then let it drip into the sump, won't the kalk loose it's potency (partially or completely) when exposed to air (specifically C02)?
The only way kalk will lose it's potency is if it's exposed to air as atmospheric CO2 will slowly diffuse thru the air/water interface and in effect precipitate out calcium carbonate. If you mix up a kalk solution and fill it completely to the top and cap it, it should not lose it's "potency". Usually, it's recommended to mix kalk nightly to ensure that it's fresh. Others use Nilsen reactors (do a websearch for some good websites) or even just a large tub of RO/DI water with an excess of kalk powder and a powerhead and a dosing pump. All seem to do well.
