Gary, JIm, and everyone - thanks for the input, all good advice! I think I can adjust my topoff system so that I get smaller amounts of dosing, more frequently.

Jim, I am also monitoring PH of the tank constantly. That's why I know that I am not keeping up with the dosing needs.

Gary, precipitating CaCO3 is one of my concerns, guess I'll need to se how it goes, and adjust as needed? I do calibrate ever month or two with PH 7 & 10 cal standards.

Thanks!