Most systems will outstrip the buffering capability of normally saturated Kalkwasser in ato unless you artificially increase the evaporation rate of your system, thusly increasing the allowed dosage of saturated kalkwasser solution and as a result, adding more alkalinity. A common method is using a fan to blow air across the water surface of the display or sump. The problem here is dealing with the ph boosting nature of calcium hydroxide and the fact that calcium hydroxide is water insoluble, which limits a normal mixture to 2 tsp per gallon of rodi. Put enough into your system to keep up with a typical alkalinity demand and ph can easily jump to 8.8. By adding vinegar to the kalkwasser, much more can be dissolved into a gallon of rodi, making the solution more potent while simultaneously reducing the impact dosing an increased amount has on ph (typically by .20-25). As an added benefit/side affect, using vinegar with kalkwasser will act as a method of carbon dosing, which will dramatically decrease nitrates and phosphates if you have a protein skimmer in your system. This could mean eliminating hair algae from a display at first but having to feed your tank like crazy to keep nutrients in the system or having phosphates become depleted and then having nitrates skyrocket because the beneficial bacteria grown from the carbon source needs Po4 to effectively reduce No3.
So in a nutshell, Kalkwasser can work fine but lacks the adjustability and precision of 2-part dosing and require more setup to keep up with higher alkalinity demand. It’s more about mixing and adding kalk a certain way and not deviating from that method, instead allowing the tank to settle at a certain dkh/cal within accepted ranges. On the plus side, kalkwasser is dirt cheap. You mentioned sodium bicarbonate and that will absolutely keep up with your tank’s demand but will require a doser, keeping records of tank usage and adjusting the dose accordingly. Lastly, don’t be surprised if you use three times as much alkalinity solution as calcium or magnesium solution. It’s normal for some tanks to lose as much as 1 dkh per day when they’re full of coral and coralline algae. I think in the vast majority of situations, if you’re losing alkalinity, it’s a great time to start dosing soda carbonate/bicarbonate. Start with a small amount, maybe 30ml per day, spread out the dosage into 4 or 8 events and set your calcium/magnesium doses 30 minutes apart to minimize stress on your critters. Test every three days and add or subtract 1 ml from one dosing time. Need more or less? Take or add 1 ml from another dosing time etc.
