I killed two starters before this one. What finally worked was keeping it small and keeping it in the fridge.
Daily routine (when baking): 20 g starter + 40 g water + 40 g flour, on the counter. It peaks in about six hours at room temperature.
Weekly routine (when not baking): feed 1:5:5, leave it out for an hour, then into the fridge. It is perfectly happy for a week, even ten days.
Grey liquid on top just means it's hungry. Pour it off, feed it twice, and it comes back. A little rye flour in the feed makes it noticeably more active.