Ph

adjust, test. wait an hour and check again. drift will be huge. for soil it dont work 100000%. fact. lemon acid i havent tried, but lemons are old hippy fake news. buy normal ph-, will last years, will give good result always. people are so cheap, 10 £ is nothing.

It's fine. Just use some cheap acetic acid -- 5% distilled white vinegar at your local drugstore or supermarket etc. Often around the house and has multiple uses. Get 3 gallons for a few dollars. Strength of acid is irrelevant once diluted. a pH of 6.5 (or whatever) is the same whether you used acetic acid or lemon juice to get there. It's a balance of h3o+ an oh- and it cares not what provided the proton or took it away. pH balance is a rose is a rose. What i would worry about with the many choices is whether or not it interferes with ratio of nutrients. So things like sulfuric acid or phosphoric acid could shift your intended ratio of nutes. More concerning in a tightly controlled soilless or hydro context. get a 3mL or 5mL pipette and dosing is easy. e.g. tap around 8.4 might need 2-3mL of acetic acid per gallon, give or take to get to 6.3-ish... Once you map it out relative to your tap or tap+fertilizer, it'll require the same dose each time -- assuming you don't change fertilizer products or drastically shift your fertilizer dosing or your tap water doesn't shift, which obviously all of those things do occur, occasionally. Any change in fertilizer or if your tap pH shifts, gotta go through the process of slowly adding 1mL or 1/2mL and re-testing pH etc until you reach the desired ph-balance. My tap pH shifted one winter (8.4 to 7.0), and i killed 160 USD worth of seed, because i added the 'normal' amount of acetic acid I always added previously without a spot check. I can laugh about it now, but quite angry and frustrated back then. Had about a 20-25% success rate, if i recall. Spot checking is well worth it. the ferts i use automatically ph-balance... an attribute worth looking for, but at some point most use water-only for 'something.'

Citric acid is too strong and will be of detriment to your microorganisms. Although it's effective. There are much better options.

i do. i use a small bottle from supermarket to get ph from near 8 to 6.1-6.3. It works but is not longtime stable, which is no problem here. My Soil has something under 6, so it balances itself out. My Drain has a ph of 5.8.

It does work but would get really expensive unless you have a lemon tree or bottled lemon juice or something. I need to add cal mag to my water, and found that it does the job of ph ing my water perfectly from about 7.5-8 down to 6.5. I bought a ph adjuster an rarely use it now. That stuff a very tiny amount goes a long way. I believe its phosphoric acid.

you can. it adds in a few other things then just a PH down. like sugars, esitonal oils and lemon scent, Its not a super strong acid but it can work. Some main brands PH down is a mix of citric and phsporic acids.