Agree, aim for 5-7 and you're good. Hard to say if your TDS meters are off in the same direction or not (hobby grade units are almost always off except when you first calibrate) but they provide a framework to go from. If dosing the same volume of water every time, you can dial it in pretty close with your meter from here on out. I bother to test GH 2-4x a year at most these days. SS and Dennerle make very consistent batches in my experience.
Nothing good happens fast in an ecosystem.