When I first got started in SW
I stored my mixed water in what I thought was a tightly sealed container. After a water change I lost 3 fish. Being a noob a waited a couple of weeks and added more fish and used water out of the same container for the next water change. Of course I lost all my fish again.
My container wasnt sealed and I was killing my fish with bacteria from the stored SW
. Since that I NEVER store SW
for more than a few days without using it.
Im not the sharpest tack in the box, so my experience wouldnt necessarily apply to you.