Mixed Saltwater

I've got my saltwater mixed, heated and have a power head in a trashcan with a lid on it. I plan on keeping 15 gallons or so at a time. How long should it keep like this, and what tests should I do before doing a water change with it? Thanks.

 

They claim not to use your water until its mixed for 24 hrs but not to let it set for more then 3 days. I use fresh water for top off and mixed for water change. I lose about 8 gallons a week so I just replace with fresh without losing salinity. If you always add salt your going to have a high salinity real fast. Hope this helps

 

Tests: Temperature and Salinity.

How long to keep it: Don't mix up more than a water change worth. Then only keep it until your next water change. It gives you enough on hand for an emergency but you would never have ASW in a holding container that is older than your water change schedule. In theory, you can keep it as long as you like, just keep it stirred/mixed.

 

Thanks folks, very much appreciated.