| | Re: Macro and Micro going bad
Macro solutions - Normally stable and do not go bad. Can be preserved w/ ~5% Excel.
Micro solutions - More unstable (due to the intrinsic nature of Fe). Store in the dark or refrigerate. Can be preserved w/ ~5% Excel. If micro solutions go bad, it's usually due to mold / fungus growing in solution.
All solutions can (eventually) support algae growth so checking for algae or growth in the solutions bottles periodically is a good idea. This is also why the addition of Excel is a good idea.