I haven't experienced otherwise. Should keep it out of the sunlight in a dark place.
Dark glass is recommended, but I haven't ever had any.
How long you can leave it in room temperature?
I have never paid any attention. It doesn't spoil, although like anything else the fresher the better.
I juststarted to use CS this week and not sure how much I need long run. Can I make a small batch instead of a gallon?
I use quart jars, and when it gets down to 25%, I start a new batch. I don't require strong CS so I can make a batch during the day. Since I don't drink it, I don't use much. I have a hand held nebulizer that don't use much.
I used to make it for my grandaughter while she was in college, and my 80 year old neighbor who had an infected toe. She couldn't get a slipper on it because of the soreness. Soaking it while watching TV, she was wearing a slipper the next day, and a couple of days later it was healed.
I think you should think in terms of a quart, and see how it goes. The quart won't take as much time as the gallon.
It's hard to say how much you should make because everyboys needs are different.
Just go for it, or buy a bottle to see how it goes.