In addition to the other answers, I'd like to add a comment about the risks:
A 25% solution of NaOH in large quantities is very very dangerous. On drop in the eye and you will be permanently blind.
It is much worse than acid. Acid causes something akin to a burn that keeps the acid away from the unburned tissue below. NaOH on the other hand dissolves the tissue and penetrates very deeply. The drop in your eye will liquefy your eye.
When you pump it you'll have a lot of pressure, the solution might corrode the plastic and suddenly you have a leak that sprays corrosive lye all over you.
When you mix NaOH with water, it will heat up. Maybe enough to make it boil explosively. Hot NaOH solution is even more corrosive.
I don't know much about well treatment, if you really need to use NaOH, use at least both a full face shield and safety goggles + raingear and have someone stand by with a water hose to wash of any spills quickly. Keep kids and pets away.
I suggest you check if using a carbonate or hydrogen carbonate (e.g. sodium carbonate, sodium hydrogen carbonate) would work. These are much safer.
For the non-food grade, I would be careful. Some industrial stuff is just as clean, some is heavily contaminated. Maybe the people selling it have an analysis of the batch. In any case, make sure you rinse your system very well afterwards.