Storing saltwater

I have a 40g brute trash can with a lid that I store water in. Is there anything negative about storing saltwater in this for a few weeks until I use it all up in water changes? It is heated and has a power head pointed at the surface to break up the water and mix it a little bit. How long can it sit and be alright? Res sea coral pro salt by the way.

 

There should be no problem with the storage, the container is commonly used for such purposes.

 

I use Brutes, as long as it's covered, circulating and heated, you'll be fine.

 

How necessary is heat?

 

If you are making a large water change, very, you do not want to shock everything with a large temperature swing.

 

I don't heat my water till the night prior to my wc just so the water is upto tank temps for the wc

 

I think that's fine, as long as the temps are similar. If you're referring to heat with storage, I don't think it's necessary, as long as the water is flowing. Just heat it before it's used.