How long does unused saltwater last?

[Quinn]

I mixed up way too much water this morning for my water change, about 10 gallons extra. Can I leave it with a powerhead to keep it moving for two weeks when I do my next water change?

[spikehs]

i have ton it many times with no probs....one time i left it without a powerhead and it stunk, still used it and nothing happend. I have a 50gal container I usually mix up 1 big batch at once then dip into when i need to.

[Delphinus]

I try to always keep a batch of SW on hand, you just never know when you need some in a hurry. It's gotten as old as a month or so (stirred with a powerhead and I keep a heater in there, too) before I ended up using it for water changes and I saw no issues as a result of it's "vintage curing."