Instructions for starting and maintaining a sourdough starter.
If you are actively using it, feed every day. If storing in the fridge, you only need to feed once per week. Take out of fridge a day or two before using.
I find with my starter that I can usually do smaller feeds such as 30 to 100 starter:30 flour:30 water. But this depends on your own starter. Let it speak to you :)
Hint: I never keep track of how much starter I have at a given time. I usually guesstimate what I should feed. Starter is hard to kill (Unless you are Lisa).