I know, add enough to get the pH where you want it. But sometimes I get a big change from a few drops, other times it takes a lot more. I think I must be doing it wrong. Perhaps my $20 meter is crappy, or perhaps I’m not mixing it well enough. I’m wonder what to expect. If I have 2 gallons of water at a pH of 7.0, should I expect to add 10 or 20 drops of pH Down to get to 5.8, or will I have to add tens of milliliters?
Do a few drops at a time, shake it up then test. Leave the tester sit in the water until it stops on a number. Mine seems to be taking longer than it used to.
I’ve noticed PH up is a lot weaker than PH down. It also seems harder to hit the number when I have nutrients in the water.
Not sure this helps, but make sure the meter stops moving and also lightly tap the meter to free any air bubbles.
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I add a little at a time, stir it up good then check, repeat till it’s in the range you want. I stir for a couple minutes to ensure its evenly distributed
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Good question! I have noticed that pH down seems to move the pH faster than pH up does.
I’d do 5 drops at a time and mix the water up good and check your pH. And keep doing until you but it. My guess is it should be 10-15 drops.
If your adding nutes add them before you pH the water!
Hope this helps? Let us know how you make out!
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I have found a method that works well. I use a syringe that they use for TB skin testing (an insulin syringe will work) and use the numbers on the side to judge how much I use. It works so accurate that I do not check the pH one day, usually do but got in a hurry that day. The runoff the next day was great. Just takes a few times to get the amount right. Jerry
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Around 2-3 millimiters of GH pH down should be enough
You will always have a range difference with pH down and pH up due to your water quality. Always check TDS (PPM) of your water quality. Tap water is considered hard due to state treatment system to make water drinkable. If you can used rain water 
it will be better than tap water due to pipes, trace elements such as chlorine, zinc, chloride, boron, calcium, and many attributes that can be from build up in piping systems, but reverse osmosis water removes all these trace elements to give your plant water a 0 TDS reading which makes Ph’ing much easier same as rain water, but tap water that’s not prepared can be a bit challenging going up and down for balance pH. If you have a fish tank, fish 
water is another great candidate for plants like an aquaponic system but the fish bacteria in the water is highly beneficial microbial for plants use…you can get a water clarity test from your local environmental control department are do your testing. If you sample water from your bath tub faucet, kitchen sink, and outside faucet, you’ll find a difference in readings slightly just to understand what the water carries as it past through certain pipes. I KNOW THIS IS WAY TO MUCH FOR ONE TO DO TO GROW PLANT, but water, lights, and temperature is the primary keys to big yields, good water gives you good healthy strong plants.
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Does the water temp have anyhting to do with how the pH up or pH down work in the water? just cause ive noticed on a few things > at 25degreesC its 7. oh so it was the calabration liquid. Just wondering if the up and down were effected the same
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PH is affected by water temp, yes.
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Maybe I didn’t really answer your question…
PH can change as the water temp changes but I’m not sure the temp makes it “harder” to ph, it just might mean you have to add a little more or less of up or down.
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what i meant was say for instance you add a drop of ph down to a set amount of water in two bottles one bottle is warmer water one is cooler water will one drop lower then the other because of the difference in the temp of the water
Yes, I believe so because the H+ would be different. Whatever that means. LOL
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positive hydrogen?
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Sounds smart so I’ll go along with it 
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lol I dont know if thats correct i know H is hydrogen and + must be positive, maybe it just means ion concentration in a solution which i think is a positively charged solution but again im guessing, but thankyou for answering, i was just thinking maybe thats why the difference for everybody pHing the water some have warmer or colder water and that effects how much it drops or rises, maybe 25C is “sweet spot” for water phing and thats why its on the calabration liquid. I was only thinking about this the other day actually when i was pHing some water
If you’re using tap water, its got carbonates in it. Each time you introduce acid (pH down), the carbonates within the water dissolve and drive the pH back up a bit in the process. This will continue until all the carbonates are dissolve. It’s called the yo-yo effect. As this process is being done, less and less carbonates remain, and the strong the effect the acid (pH down) will have on the water you’re treating.
Adding acid to tap water should be done slow, and cumulatively less each time you add, as it will have greater effect. Its best to wait a bit for the these carbonates to dissolve before a measurement to be taken. The more water that you’re adjusting pH, the more time you should give.
Hope this helps
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So rain water would drop faster with less pH down because it doesnt have carbonates? @Aquaponic_Dumme