In most cases
solution has atleast 1 year shelf life. We have some really old 'like 3 years" every so on we take it out and try it. Still works well color not as dark but really close. Just be sure to keep the lid on it, out of the sun and away from heat. If you aren't going to use up
solution within about 6 months I wouldn't pour left over
solution back into the jug.