MIGrampaUSA
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Organic grower here ...pH up and down are not buffers. Whoever told you that was confused. Soil can be a buffer.
I agree with your method — nutrients and additives can change pH. Adjust afterwards.
I am skeptical of the blanket statement by some organic growers, saying irrigation water doesn't have to be adjusted for pH. That doesn't fly if you have a lot of minerals in your water. Soil is a buffer, but all buffers have a capacity. Once that capacity has been reached it can't help you.
pH up is a base. pH down is an acid. Buffers perform a chemical reaction to adjust pH.
There's good reason to be skeptical of any "blanket" statement. In my case, I use 2 stage filtered water ... 1 stage removes chlorine/chloramines and the 2nd removes dissolved solids so while the filtering doesn't change the pH of the water itself, it does remove the buffering minerals so that the soil doesn't have to work as hard and the buffering capacity of the soil should easily last the length of a full 3 - 4 month grow cycle. I'm not sure I would say the same about extremely hard well water unfiltered as this would surely alter soil pH after a couple of months of use.
A lot of whether or not a blanket statement like above is true depends on the source water. The flip side is because mine is filtered, I end up adding more magnesium and to a lesser extent calcium back to the mix than others might. Where as someone with a known hard water source might do better using nutes designed specifically for hard water. Some of the companies are offering "hard water" formulas ... not sure if they're organic or even if that matters to the OP as I've not researched them. I'm simply aware that they exist and for some growers, have changed the quality of their grows.