How Long Does Saltwater Last?

Hello

So, besides the obvious evaporation, how long does salt water last? What I am trying to do is mix a months worth of salt in a drum and keep it to pull from. The salt manufacturer states that the water should not be mixed for more than two hours or else it'll break down elements before they reach the tank. It kind of makes sense but also not. Because the tank will keep mixing it with all of the flow in it and I don't see how the corals could eat the elements, such as calcium, fast enough.

I know fish stores mix the salt and keep it in massive containers, but does it have a certain half life to it? I could keep a heater in it but worry to keep it mixed as the manufacturer says not to.

Any ideas if it'll last a month? I don't see how it could go stale or evaporate on that short period as I'll be pulling from it weekly.

Thanks for your help!

Marcos

You are right. It is common practice to have mixed salt water available on demand. 

Edited by Mark Peterson - January 08 2015 at 8:43am

Mark Peterson wrote: You are right. It is common practice to have mixed salt water available on demand.  Others may have differing opinions, but here are some of the lessons  I've learned about mixed salt water: - After it's mixed thoroughly in a container/barrel, occasional stirring is a good idea. - 60+ degree salt water for normal water changes causes no problems. The difference in temperature sometimes causes a temporary reaction, but no harm. Think of the ocean where cool nutrient rich, up-welling currents feed the reef. Of course we know new salt water has nutrients that feed the reef. (Taking this a step further, that's why, in the case of an algae problem where N and P test zero because the algae already cleaned it up, water changes actually feed the problem.) - Where possible, it's a good idea to use most or all of the salt water in the barrel before mixing up a new batch. Old salt water, especially if it has been in a sealed container for more than a couple months can have a bad effect on the animals, if it is not opened to the atmosphere and agitated for a few minutes before use. - Any object left in the container of salt water, especially true for RO water, will contaminate that water to some degree. H2O is awesome. Practically everything dissolves in water, to variable degrees and at variable rates. Metal or metallic objects can be particularly harmful. Not all plastics are created equal. Manycontain soluble compounds and others may still have chemicals on their surface that helped them release from the mold in the manufacturing process. It's a good idea to clean plastic containers and objects with mild soap and a good rinse before aquarium use. - When changing to a different brand of salt mix it's a good idea to change over slowly in 4 steps: 1st water change use 75% old with 25% new salt mix 2nd 50% old with 50% new 3rd 25% old with 75% new 4th 100% new salt mix Hope this info is helpful. Aloha

Thanks Shawn, I am sticking to the small batches since I can only store a large quantity too far from the tank.