If you are concerned, scrape off the white surface and refresh the starter, once again then use it.
After using the starter, spread some of the starter on a sheet of parchment paper and let it dry out at room temperature. Crumble this and place it in a clean zippered bag and keep this in a cool, dry place as a reserve starter. It will keep for years.
Do you keep your mother in the fridge or at ambient room temperature?
Do you keep it covered to hold the moisture?
How long since your last refresh?
I've refreshed my sourdough for 2-3 days. It was kept in room temperature and yes, i covered the jar.
How old is your starter? What is the hydration? Have you ever used this starter? What is the flour?
Ford
about 7-8 months,
50% flour and 50% water i think,
yes i have used my starter from the beginning
wholemeal 2000
If you are concerned, scrape off the white surface and refresh the starter, once again then use it.
After using the starter, spread some of the starter on a sheet of parchment paper and let it dry out at room temperature. Crumble this and place it in a clean zippered bag and keep this in a cool, dry place as a reserve starter. It will keep for years.
Ford