Your meter is reading a decrease in Ph caused by adding acid to the water.

What's connfusing?

willard thanks for reply

but dose that sound like a large amount of vinergar to drop only .6 of a ph
elnino

I think your meter has a problem.

I've got a HANNA and I did the same thing:
Tapwater 1L, pH=8.6
Add 50ml vinegar (5%), pH=3.1 !

Just remember that pH readings are exponential, not linear.
a one point change is 10x the acidity. a 2 point change is 100x the acidity.
I'm not going to try to calculate what the pH drop should be, just thought I'd pass that piece of information along.

What can you use to bump up (or down I suppose) the pH? From a 5 to a 6.5, say.

Sodium bicarbonate (kooksoda) is cheap & easy, but you can also buy some "pH-up".

Ph down:
Phosphoric acid
Citric acid
Ammonium bisulphate

Ph Up:
Potassium carbonate
Potassium hydroxide
Potassium silicate

The general kitchen stuff, ie, vinegar, bicarbonate work very poorly in combination with hydroponic nutrients.

"work very poorly in combination..." do you mean lock-out? Or do you have to add it every day and it is a pain kinda poorly?

I've always used it (vinegar & bicarb) and have never had a problem.

I've tried using vinegar and bicarb and it (Ph) bounces like crazy for about an hour and then the nutrient returns to where it was before you started. My municipal water quality is pretty good with low mineral content. If you are using pre-mixed nutrients (I do), the problem is worse.

Bicarbonate will also plug up fluid passages because, if you don't mix it like crazy and let it sit for a couple of days, it's not fully dissolved.

Bad water quality and/or bad growing medium will also effect Ph.

I have here some information about the pH buffering capacity of bicarbonates and acetic acid.

Carbonate Buffers
Acetic Buffers

Hope this helps to explain that there is nothing wrong with the use of these chemicals in hydroponics.
Note the buffering ranges.

Thanks everyone, but now my brain hurts... Is there a useful reference or reading on this subject that you folks can point me towards?

I am just starting a DWC garden in my basement for my first try at hydro, and will be growing lettuce, spinach, and other salad greens under a 400w HPS. My tapwater is around PH 7, and My reservoirs(2) are 15Gal. I have had airstones going in the tapwater for 2 days now to off-gas the chlorine, and I plan on adjusting the PH before I mix in the neuts(GH Flora).

So... how much vinegar will it take to bring 15G of water from ~PH7 to ~PH5.5?? I know there is no absolute answer here, but I am hoping for a starting point.

Thanks for any help

cruelsun wrote:
So... how much vinegar will it take to bring 15G of water from ~PH7 to ~PH5.5??

I use a 5ml syringe for this. Start with 10mL 5% spirit vinegar and see what happens. Make notes for future reference.
I also think that you may need to check the pH after you've added the nutrients. They may well affect it.

Thanks for the tip Greystoke, I did as you advised, and made 4 separate additions aver 4 hours or so last night, each time re-testing at 5, 20, & ~60 min afterward. The ph reacted to the vinegar each time then bounced slowly back up. I added a total of 45ml of 5% vinegar over the 4-5 hrs, and now 14hrs later it is at ~6.5... Is that a reasonable result? Should I try adding larger volumes of vinegar at a time?

That's quit a bit of vinegar. That shouldn't be. Your nutrient must contain a strong buffer. {{gwi:996791}}
Yes, by all means add more at once, you will get there, but . . I'm now thinking about what willard was talking about: "I've tried using vinegar and bicarb and it (Ph) bounces like crazy for about an hour and then the nutrient returns to where it was before you started."

I talked to a friend who does a lot of work with tropical fish, and he seems to think there is PH buffering in our tap water. I have not yet mixed the neuts into this water. I've been running air thru it and getting the PH right until the seedlings are ready.

But the punch line is that I did as I suggested above and added 20ml after my last post a few hours ago, and the PH shot right to 5.0 and has held fast there... Feast or famine... I have to top off the reservoir with 1-2G of tap water before I mix in the neuts, so that should bring it a bit closer to 5.5.

I have another 15G reservois to play with soon, so I will try to add 20ml or more at a time and report on the results. If there is a buffering agent in the water, maybe I need to "overwhelm" it instead of tickling it with a little acid at a time.

Folks, your info here has saved me - I set up an ebb and flow system tonight - I used rainwater from plastic barrels and it's got a pH of 7.8 both before and after adding nutes!! I used two different metering systems - a Hanna tester and some decent spa strips. I have some pH down, but the only instructions were to add a drop at a time - hardly a rought estimate, plus the toxicity situation demanded goggles and gloves - I have serious health problems and it made me nervous to say the least.

I am new to hydroponics and this is my first set-up except for an AeroGarden. I have 6 gallons in my tank - so after reading all this, I put in 10 ml 5% vinegar and will check it in an hour. I have new transplants in this so am concerned at problems that will shock the plants. Dirt, I understand. Water, I don't.

I appreciate everyone for the posts here because without them I would be an unhappy camper right about now after several hours stressing out and trying to find answers.

Thanks