Think about what you just asked. PH up or down are like $10 for the big bottle...spend the money for the right shit.
pretty much any gardening store will have it im sure you have a grown store around you some were short of that check the web
hydroponics shop. The stuff lasts a long time. Since I switch nutes I find myself not needing to change it.
Ph down us fulvic acid or something along those lines. And you know if you have high ph tapwater you could use that for ph up here and there. You can buy the hydro companies ph products at your local grow store or Amazon
ONLY if you are growing IN the pool. If not, then I would suggest getting the proper tool for the job.