pH of your "waste" isn't anywhere near as important as a lot of people seem to think it is. Stuff changes over time. If you mixed up a batch of nutrients ahead of time, began madly aerating it with a big air pump and lots of air stones and/or by using an aquarium power head, tested its pH, then poured some into a glass and let it set out overnight, you might even find that its pH ended up being slightly different than that in the original container that was still being aerated.
As your plants grow and develop healthy root systems... they'll excrete waste products via those root systems. That is going to affect the pH of anything that happens to remain in your "reservoir area." Also, unless you become some kind of mad (plant) scientist and suddenly become able to feed the plants exactly what they'll end up consuming that day, no more, no less... then the things will end up consuming a higher percentage of certain elements than others (percentage of what started out in the nutrient solution, I mean). That will change the pH of what remains, too, just like it changes when you - for example - add more FloraBloom when mixing your solution up.
If you grow cannabis in a DWC setup, where your plant lives in a (relatively) large reservoir, such things become significant. You might even get to the point where you... instead of adding water to your reservoir each morning to replace the liquid that was used, you check the pH, make an educated guess about what was used, and replace the lost liquid with a "modified nutrient solution," thereby - to some degree - actually replacing both the consumed liquid and the consumed nutrients, and extending your time between complete reservoir (solution) changes. Plus, if you monitor the solution in a DWC reservoir on a daily basis, observe that it's 5.89 on Tuesday, return on Wednesday to check it, and find that it has suddenly dropped to 4.20, lol, then you'll probably immediately start trying to deal with the sudden "bloom" of bad microbial life that just colonized your reservoir.
However, you're growing in a "hempy" setup. You are basically replacing the liquid in your small reservoir every couple days (give or take). You're probably also, in the process, performing a "mini-flush" of that reservoir each time you do. And, with synthetic nutrients, and reasonable good hygiene practices, you shouldn't have to worry about microbial life - if so, a little H2O2 will take care of things AND give your plant a nice little oxygen boost in the process.
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