Usually it works well to store greens dry, not in water, unless it’s just the stems in water, like flowers? Things may be going slimy faster in water. The way I learned to keep things really fresh was when you get everything home from the store, dunk everything in a sink full of water with a cup of vinegar mixed in, then dunk again in fresh water, then dry completely before putting in the fridge. If you can have a little air in the sealed bag it also helps (the spots where the bag clings to the lettuce then to turn slimy faster). I know that wasn’t really your question just thought I would share!

Also spinach is fine to feed in moderation, so as long as it’s not most of the spring mix it’s fine to leave in. And definitely fine to pick some out as you see fit. Spinach is recommended in moderation due to calcium and oxalate content, but it’s not toxic or anything like that!