You might appreciate this. I just brewed a weizen last weekend and used a decoction mash. That's the most traditional method from what I've read. I mashed in at 113*F and then decocted to raise my temp to 122* then another decoction for 149* and the mash out decoction of 168*. I'll be honest.... I didn't always hit my temp with one decoction, so I had to take another, boil it, return it and rinse and repeatedly until I got my temp. I have no idea how this batch will turn out, but it was a great learning experience.
As far as your pH concerns, weizens are typically higher pH beers. So 5.59 is perfectly acceptable. I wouldn't add any acid at all. If you do add acid, add lactic (as per Martin's suggestion) and do it only after your acid rest.
I am curious though, why are you doing a 45min acid rest? I don't think you'll get any additional benefits from going longer than 20min. Just curious.
When you drink it, please let us all know how it came out! I'd love to see the result. I'll share mine when it's ready too.
Good luck, happy brewday!
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