Good luck on your run!
To be clear I'm not a heavy user of the products, despite my vocal endorsement. I typically will only use 1 nuun tab on a ~20 mile run, and maybe 2-3 for a 50K. Then, during the week, I'll only pop one if I notice my hands swelling or notice that I've gained a few pounds.
One of my big revelations that I might have been hyponatremic all summer long my entire life was that I was feeling like crap for a couple of weeks, and then went out for an incredibly salty Indian dinner. Despite overeating, and drinking massive quantities of water, I dropped six pounds overnight and woke up feeling great. It was a couple of weeks later that my friend gave me the Nuun. Much as I love a good Masala Dosa, the Nuun is easier and cheaper.