Whisk together kefir, water and starter, until starter is completely dissolved in the liquid. In 1/4 cup increments, add rye flour, mixing well after each addition.
Cover tightly, and allow to ferment 8-12 hours, or until very bubbly. It's best to use a glass bowl because the bubbles in rye batter don't form on the surface, and it's convenient to be able to see the inside of your batter.
When ready to make pancakes, start preheating the griddle or pan.
Mix egg with sugar and salt; add to the rye batter; mix well.
Add baking soda; mix well again. Allow to rest for 5 minutes for soda to react with the batter (you will see the batter rising and softening quite a bit). Adding baking soda also tones down the sour taste of the pancakes.
Pour batter on a hot griddle. I use a 1/4 cup measuring cup, but the size of the pancakes is up to you, so use what you'd like.
As soon as the top looks like it's starting to form a film and is no longer dripping-runny - flip the pancakes, and cook until golden. If you don't plan to serve them immediately, place the pancakes in an oven at 250ºF, to prevent them from getting soggy.
Serve with sour cream mixed with a bit of pressed garlic, herbs like dill and chives, salt and pepper; or with butter and honey for a sweeter version.