Cilantrillo said:

Well, there's H in H2O. ..
By definition, "In chemistry, pH (/piːˈeɪtʃ/) is a numeric scale used to specify the acidity or basicity of an aqueous solution. It is approximately the negative of the logarithm to base 10 of the molar concentration, measured in units of moles per liter, of hydrogen ions. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion."
Deionized or R/O water is acidic in nature. There's indeed something in R/O water...and the meter picking up a low-pH reading is spot-on.

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MedicalMG said:

Just to throw this out to you but baking soda is not buffered. They do basically add baking soda to the osmosis buffer but they also add acids to create a buffer (you add acids and bases to create a buffer, this would be the difference between ph down and just straight muriatic acid).

http://chemistry.about.com/od/acidsbase1/a/buffers.htm

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RoeBuck said:

I agree, adding acids will create a better buffer. But from what I've read, just baking soda alone is effective and so far that's proven out for me. Here's the link to the information: https://manicbotanix.com/maximum-yield-hydroponic-gardening/. Unfortunately this site won't allow cutting and pasting or I would have pasted in the pertinent information. It's about 3/4 of the way down the page, under the heading "Correcting/Creating Alkalinity in RO water with Carbonates".

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