How long until nutrients go bad in water?

Very true. Especially if you are using organic nutes. They will breed bacteria and mold if left to sit in a container too long.

Chemical nutes can be stored for a while, but they too can grow bacteria and mold if left to sit too long.

you are better off mixing what you need as you need it.

 

How bout leaving some superthrive in water for a day or two??

 

2 days wont make a difference unless you have something wicked floating around in your room already.