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I just finished baking Baking Soda. I need to raise my Alk (5 dkh). Is it OK to put it in a zip lock bag after baking or is a jar/container better (I will have to go buy one)? If I leave it out, will it collect CO2 again?
I'm not too much of a fan of using baking soda, baked or not baked, to attempt to control alkalinity.
Before you try this, make sure your other water parameters are good, especially magnesium and calcium. If they are not good to start with you can add "tons" of baking soda, and get very little long term effect. It's very easy to trhow the water out of balance, and you'll end up doing massive water changes to fix it.
I recommend you test your newly mixed SW, and see it the parameters are good. If so, make water changes, if not, change your brand of salt till you get good parameters, and make water changes.