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[.]

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[Bruce Rittel]

Even after that amount of time it should still be OK! But if you prefer to check it - simply add one half a fluid ounce of it to 1 gallon of water and check its pH. It should read approximately 1.1 pH. My local water here is a 6.8 pH.

Somtimes if its exposed to extreme cold - crystals will form in the bottle. They are small but can be seen. If you see them, simply place the bottle in a warmer area, and shake the bottle as they begin to disappear. When dissolved - the Acid is again usable and should be fine.