OP posted using a controller so constantly shifting buffer values are a problem if deciding to alter parameters. The KH value and resulting pH will be constantly rising gradually as the solid is dissolved into solution adding buffer, then only to drop with the next water change. Using a controller that's a nightmare. I prefer static changes I can control. Betting the OP would too.
CaCO3 doesn't mix very well in my experience using it. The reason I use baking soda is solubility,cost, availability and consistent results. No issues with it precipitating out of solution either. The sodium content of baking soda isn't a high enough concentration at the level I dose to effect flora or fauna. Dosed at water changes to test out as 2dKH is enough to maintain stable PH values in the 7.0 - 7.4 range without CO2. I've only once seen tested values drop after setting parameters and that was after long term neglect on a trimmings tank.
To increase KH (using leveled teaspoons)
1/8 TSP : 6.605gallons = 1dKH
1/4 TSP : 13.21gallons = 1dKH
1/2 TSP : 26.42 gallons = 1dKH
Potassium carbonate or calcium based are our 2 best choices looking for a buffer.
BS is the cheapest, has great solubility and is readily available.
Thanks for the information. I actually started with sodium bicarbonate, but started slowly initially. In my 75 gal tank, I added a little less than 1 TSP and it did not make much change. This morning, I added 1 TBS, which by this number should raise the dKH by 2. This should bring my total up to about 3 dKH. About 30 minutes after adding the TBS, the pH did raise to 5.8 while adding CO2. I will be checking after I get home this afternoon. My CO2 is on, but at a low rate and with the pH controller, will not be dropping the CO2 below pH 5.5. To date, I've never seen my CO2 drop checker turn color - it is still sitting at a dark blue. Granted, I realized that my drop checker is on the intake side of the tank. If I move it to the outflow side, it should measure a higher CO2 when adding.
I've hoped to avoid manually adjusting the dKH/dGH/pH, but this is just too low to use the pH meter and due to the driftwood, fluctuation at water changes. (yes, I'm sure there will be suggestions to just use a bubble counter and watch the fish... If I go there, I'll go there.)
What removes bicarbonates from water? Obviously WCs. Do plants break it down at a noticeable rate? Do I need to continually by dosing BS?
So, I'll check this evening and see where the pH and dKH is sitting after a day of circulation.