Above 7 dKH and less than 10 dKH. Keep in mind bicarbonate, calcium and magnesium carbonate can be used and depleted independantly. Always monitor them with some frequency and be prepared to dose, indepentantly if needed.
Hello and welcome to r2r!
I like to keep my alk between 7-9 but that's just a personal preference. I have seen tanks anywhere from 7-12 dkh. but that's not the most important part, stability is! pick a number (within the acceptable range) and stick to it, I would suggest a dkh of 8.
You don't want it to fall below 7, and maintaining it above 9 or 10 can cause a lot of waste and precipitation. I find between 8 and 9 to be a good sweet spot that gives you enough wiggle room so you don't ever go below 7 but is also low enough to minimize precipitation when dosing.