The problem I found with keeping solutions was:
Storage (have to use 'black' containers, or store in dark cupboards)
Using the solution: Because I was only using 1/2 litre containers, I couldn't dissolve the required amounts (had to shake like mad before dosing).
Mould! <- thus someone mentioned having to keep it refridgerated.... I'll let him tell the wife that then.
Poured all my pre-mixes down the sink in the end & now simply dose dry, straight into the tank using small measuring spoons.
You live & learn.
Andy