If it's hot in the kitchen (I ferment on the counter so I don't forget about the ferments), I ere on the side of caution and use quite a bit of salt. After a few days I taste the brine. It should be starting to sour. If it's clearly too salty, I just add a bit of fresh water to the crock, taste again, and repeat.

I taste it every day and refrigerate the ferment once it's at the right sourness.