Why freeze. Macro fert solution should keep for months in the dark. All in one solutions will not keep. Keep two stock solutions:
1) For Macros, 2) for Chelated Iron & other trace elements. Keep in the dark/Black containers.
I have mine attached to a doser and seem fine however im a bit concerned the bottles are not shaken up every day and basicly left for a month doing there own thing not sure if it makes any difference i make up a dozen bottles or so and just keep changing them over when needed but not sure if they stay fresh was thinking of chucking em in the freezer not sure if they would still be ok though