pH drop 6.5->4 with MSU RO/DI fertilizer?!?

[tropterrarium]

I just got some MSU "pure water" fertilizer form First Ray. I use a DI system with TDS of ~0-5 after pH adjustment with KOH from dosing pump. After adding a good teaspoon of the fertilizer to the 2.25 gals of water, pH dropped to 4! Not good. I was under the impression that the pure water formula was pH balanced for pure water in the pH6.3-6.5 range [certainly not 4].
I could get pH back up with adding 1 teaspoon of Protect, but got the pure water MSU fertilizer to avoid that adjustment in the first place. It's no improvement over the Dynagrow+Protect I have been using before.

Questions:
- Is my assumption that pure water formulation is pH balanced around 6.3-6.5 wrong?
- If so, what is the point of pure water formula?
- Or is First Ray's no good?
- Or do you make a stock solution, adjust stock to pH 6.3-6.5, then add that to DI water? Does that work, or will pH change cause settlement of certain compounds (good old solubility products from chemistry)?