MAybe a silly question, but how long can mixed water last

[Nocturnal]

Basically I mixed a few gallons of water a month ago and stored it in my cellar in a closed container (cool dark area). Is it OK to still use it or should I mix a new batch?

 

[Greg Hiller]

Okay to use. The thing to keep in mind for salt water is that you really don't want to try to seal it up tight. Areas that don't have any oxygen getting to them can form hydrogen sulfide as the sulfate is reduced to hydrogen sulfide by bacteria in a really low oxygen environment. Even if hydrogen sulfide forms, if there is not a lot of it if you circulate the water with a powerhead, or even better aerate it with an airstone, the hydrogen sulfide will disapate.

Partly the answer to your question depends upon what you are planning to do with the water. If you say....10% water change on an established tank I say, 'no problem'. If you are using the water to raise larva clownfish, or some type of invert, then I'd say you might want a fresh batch.

 

[Nocturnal]

Gotcha, thanks.
I was just going to use it to top off the tank and only like 2 gallons or so