Maintaining a sourdough starter There seems to be (much like everything else) different recipes, though most call for equal parts starter, flour and water for maintenance.
However, one particular (and popular) blogger calls for the following recipe:


  Scoop in 50 grams of the mixture from the jar that fermented
  overnight. To this, add 50 grams rye flour, 50 grams all-purpose
  flour, and 100 grams water


Is there a "correct" answer here, and what's the difference between the two recipes?
The difference is the time until the starter matures. Without going into the maths behind, just remember that growth is exponential, not linear.

My favorite source (in German, sorry), uses 10-20 % of the flour weight. That means that the starter will need feeding about once a day, as opposed to the equal weights approach, where you feed twice a day (or even thrice, if you have an exceptionally active starter). I wouldn’t go below the 10%, just to make sure nothing unwanted can get a chance.

So “correct” is what fits your feeding and baking schedule, as long as the starter ratio is somewhere between 10 and 100% of the flour weight and you give it the correct time to mature.

Remember - the principles of sourdough have been used by humans since way before the invention of scales. So while weighing is something we often recommend (at least as in “use a scale, not a measuring cup”) for bakers who aim to get reliable and reproducible results, learning about the characteristics of your specific sourdough, its demands and behavior, and how to tweak it to match your needs, is in the end way more important than the ratio of starter to flour.