Hi Lynn, since you seem to have two containers of sourdough going, it's probably wise to give up on the one that has mold growing on it. However, I would take care to cover your remaining starter container more carefully with either plastic wrap or a lid, as it's not helpful for it to develop a crust on top. The reason we say to "cover loosely" isn't because the starter needs airflow in order to ferment properly (it doesn't), but because fermentation gases can build up in a tightly closed container and cause the top to pop off. Plastic wrap will flex, and as long as your container has sufficient head room for the fermentation gases to gather above the level of the starter, and you open the container now and then to vent the gases, a lid shouldn't cause any issues either. 

You didn't mention what your current maintenance routine involves, but here's the starter feeding routine we normally recommend. It's perfectly normal for a starter that has been fed at room temperature to rise up over the course of several hours and then reach a peak. It will hover at the highest point for a time, and then, if not replenished (fed again) will gradually collapse down to the level it was right after being fed. Ideally you want to feed your starter at its peak of rising, or just as it begins to fall, as this will keep yeast activity vigorous. Allowing the starter to fall significantly between feedings can lead to more sluggish yeast behavior.

If necessary, you can tweak the ratio of ingredients in your starter to allow your room temperature feedings to line up closer to that peak of rising. For example, a 1:2:2 or even 1:3:3 ratio of starter:water:flour (by weight) will slow down fermentation in warmer months, while our standard 1:1:1 ratio may work better when it's a bit cooler in your house. The goal is to find a twice a day feeding routine (when your starter is out of the refrigerator) that allows you to replenish it when it's close to the peak. 

I hope this helps! Let us know how it goes. 

Barb

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