Is this mould?

Four questions. You do not need to photograph anything and you do not need an account — you are probably holding the jar.

That is kahm yeast. Annoying, not dangerous.

A flat white skin is kahm yeast: a yeast that grows on top when a starter has been left alone too long or stood too warm. It is not harmful, but it does mean your starter is hungry.

What you do now

  1. 1 Spoon the skin off and throw it away.
  2. 2 Take off the top layer of starter too, until you see clean dough.
  3. 3 Feed what is left 1:2:2 and put it a degree or two cooler.
Do the starter check Read why mould goes deeper than you can see Start over