I am alittle confused on mixing saltwater. I am now cleaning to many tanks so I want to have saltwater premade. I currently have an R/O unit that fills an 86 gallon resvoir. I want to upgrade and have a 50-100 tank with made saltwater. But if I mix the salt and water what do I need to be aware of to insure the water is still good when I use it? How many days is the salt water good for? Should I use a pump to keep it circulating? Should I get a container that does not let light in? Is there anything I am not thinking of? I would appreciate any help you could give me thanks!