I found an inexpensive ph down and up kit
Well first off a couple things if you are using water from a tap you have to do a couple things. First if you live in any kind of populated area you probably have chlorine in your water. This is bad for the plant. So you have to put it in something and leave it out for 24 to 48 hours to get the chlorine out. Next you need a ph Reader. In soil make sure the ph of the water is 6.3 to 6.8. I will put a link on why that is important. Now to answer your next question I need more info. Do you know what he used for the soil. Because if it’s a super soil then you shouldn’t really need anything till flower. But if he didn’t then I will put a link that should be good. Ph up and down for the water Standard Hydroponics pH Up and Down Kit - 10 Ounce Bottle pH Adjuster for Hydroponic Systems, Coco Coir Even Soil. https://www.amazon.com/dp/B07NQTSP2Q/ref=cm_sw_r_cp_api_glt_fabc_2W05N3BSPTPTKPYGH1W2?_encoding=UTF8&psc=1
Nutrients for the plants
FoxFarm Liquid Nutrient Trio Soil... https://www.amazon.com/dp/B07TH2FMP3?ref=ppx_pop_mob_ap_share
Link on why ph levels are important
Ahhh... Damn this is a really good question and I don't know the answer to it.
I buy all my pH up/down from the pet store in the aquarium section or on Amazon. Some of the chemicals used in the pool supplies may actually kill the plants. They can be liberal with actual chemicals because it's common knowledge not to ingest pool water but I don't have a solid answer for that one. It all comes down to what the products actually use to balance it out