How long can you store salt water?

So I totally scored and got this Nalgene tank from work. It was past it's usage life at work so I was able to take it home. Nothing wrong with it. It has graduations so I can fill to 200L (55 gallons) and make salt water. Luckily my reef crystals 200 gallon comes with 4 bags, so 50 gallons each. I can easily make 50 gallons with probably zero or very minor salinity adjustment. I'm thinking maybe 25 gallon water changes on my 90, every 2 weeks or so.



But can I store salt water for a month? Will it grow bacteria sitting in the dark in this tank? Usually salt inhibits bacteria but obviously not so in our live aquaria so I'm curious on how long people think is okay to store.