Its hard to explain things for me like this also. I get caught assuming people understand why im saying what i amI'm sorry I was not more clear in my meaning.
In 5 gallons of RO water, you add 1 drop of 85% acid, that ph will swing wildly. Same for base.
Doing so in a water system other than your RDWC can actually be helpful to kill off some microbes, and is a feature of using small amounts of water without a buffer and concentrated acid or base. For example, you kill e-coli at PH of 3.5, no heat or UV or caustics needed.
Add Acid - PH pegs to one end. Then bring it back down with a base, locally, right around the drop you added, you will peg it the other way. As they mix, PH will become in the right range and form a buffer.
This see saw needs to be avoided in the RDWC. Thus the comment to pre-dilute and carefully titrate.
It was not my intention that you TRY to do this in your res lol. But I can see in my clumsy wording how that could have come across.