Cultures will occasionally not take or will crash for no reason so it best to have more than you will need. Once you have been doing it for a while, you will be able to judge the number you need. I personally set up a minimum of 4 - 8 quart jars a week. Discard the culture at once. Any cultures that mites are found in should be immediately disposed of.
Cultures become susceptible to infection once the production starts to reduce.
If a mite infection is discovered, remove the infested cultures and store the remaining cultures on paper treated with lidane. This will act as an insecticide. An alternative to the insecticide paper is to store the cultures in a shallow pan with water in it. MOLD Don't worry you will get some mold every now and then. Especially if you use one of the homemade mixes.