Cold saltwater
 

I have a partial bin of saltwater premixed ( I mixed way to much )from a couple of weeks ago. Salinity is bang on to the tank. Other parameters are good, only thing is that it has sat circulating but unheated. Can I heat it and use it for a WC? or is it garbage?

Should be fine...

imo there's no point in heating stored water, until right before introduction into the tank. Or if you do small changes frequently like me, you can just add it in cold.

I never heat my water before putting it in my tank and have had no probs, I change 4 to 5 pails every 7-10 days in my system.