What is the best pH down product?

lemon juice is great and natural and also great in a gin and tonic !

IMO, hitting the lower band then rising throughout the cycle to the next full feed is basically exactly where you wanna be I use Bloom City's Pro ph down. it has everything listed below in it, which is key IMO because ph buffering is literally nothing but attrition... bonus of using this (not just acetic or citric) is that you will be adding phosphorous in trace amounts

I use and swear by drip hydro ph up and down. I use a tiny amount and lasts long af. One of the better I've found. Tried a bunch of them iver the years.

Acetic acid is readily available and cheap (5% white distilled vinegar). C, O, H ... nothing that will throw anything out of balance. Get a 3-5mL pipette for dosing per gallon or liter...larger measuring utensil needed for reservoirs, of course. 3-5 dollar 3-gallon jug from local grocery store will last years. you absolutely do not need to overpay for branded ph-up or ph-down products. Bunch of vultures taking advantage of people's lack of science education. Cheap and available locally is your only concern. There are plenty of good options.

I use lemon juice

hey 👋 Personally, I don’t use any myself ; I just asked a buddy who grows hydro : he recommends Platinum and TA. Plagron, at a stretch. Definitely not GHE or BioBizz, they’re too unstable.