How Long Does a Fresh batch of Saltwater last?

[themastr]

Hello Everyone

I have a project I've been working on and it's an automated water exchange system.

I just have one question? How long will a new fresh batch of saltwater last? I'm planning on keeping it in a 55 gallon drum all premixed, aerated and at the right temp. How long before I have to use it up?

Anyone who can help or has this setup can you please let me know.

Thanks

Erick