Getting VERY different results testing my pH-corrected water

Hey everybody,

I've been having what seems like pH problems, which I describe in another thread.

So today I did a series of experiments. My tap water is pH 8,2, so I used that as a reference. My pH-down is 38% nitric acid. What I did was that I filled a series of 1,5l bottles with tap water, and then added different amounts of nitric acid and then tested the resulting pH. To my surprise, the results were VERY different even when adding what seemed like the same amount of nitric acid.

6 drops yielded a pH of 7,3 - 7,4 - 7,2 (I did this experiment three times)
7 drops yielded a pH of 4,8 - 7,5 - 7,1 - 6,9 - 5,2 - 6,1 - 5,5 - 5,2 - 7,5 (I did this experiment nine times)
8 drops yielded a pH of 4,7 - 7,0 - 4,6 - 4,0 - 4,2 - 4,1 - 4,0
9 drops yielded a pH of 7,2 - 6,4 - 4,3

As you notice, I did many experiment with 7 and 8 drops. Now, I go to med school so I am quite familiar with chemistry, and I can't for the life of me figure out why my results have such an extreme spread and inconsistency.

To distribute the drops of nitric acid I am using a 10ml syringe very much like this:

I have shaken the pH-down bottle before the experiments.
As far as I know the drops are supposed to be almost exactly the same volume if they are from the same syringe. This is driving me crazy, and my plants are suffering greatly because of the unstable (and probably a little high) pH levels.

Please give me some insight before i go crazy!

Peace out!

Oh and by the way, the pH meter I am using is this one:
http://kinglead.en.made-in-china.com/offer/AoHnaCGOOfpe/Sell-pH-Meter-Model-PH-009-I-.html



I use my tap water as a reference to make sure it is calibrated, but I have also used distilled water. And yes, it is not a super-high quality pH meter and no, I don't have a real buffering solution - BUT, my pH meter gives correct and consistent results when testing fluids with known pH, so I have no reason to doubt it. And even if it's not 100% correct, it clearly shows that there is a great spread in my "pH-corrected" water and that, in turn, is consistent with the fact that I'm suffering from pH problems in my grow.

So it's not the meter and I can't for the life of me think that I'm distributing unequal amounts of pH-down, and I shake the bottle before use so the pH-down should be a homogenous liquid. What's left? Nothing!?

You cannot use tap water as your control, you just can't. you have to use PH 7 calibration solution AND ph 4 Calibration solution. You also need to let the PH pen sit in the solution for a minimum of 5 minutes before taking your reading. One other thing, the PH pen you are using is a P.O.S. Try a nice Hanna, Oakton, or Extech meter, they will last you for years and are high quality. They cost more than $100.

Well, I basically have pH 7 and pH 8,2 calibration solution and as I said, I don't think the pH meter is the problem. Besides, I have absolutely no money to spend on another pH meter, so I just have to work with what I've got. Even a bad pH meter would not give this kind of spread without reason.

So basically you have no friggin idea if you meter can even calibrate to even measure acid? FYI just because it is distilled water in no way means it is PH 7. And how do you know your tap water is PH 8.2? Did you use a high quality meter to take its measurement first? Tap water can vary in its PH too, the city may decide to use different chemicals from one month to the next, wells can be changed by groundwater swells etc etc. Now to PROPERLY calibrate your meter you need 1 acid and 1 neutral, we don't care about base because MJ plants won't grow in a base environment. Until you have your electrodes PROPERLY calibrated then its all just a big guessing game.

Is the temperature of the solution the same every time? Are you measuring it?

Tap water can have dissolved minerals in the water which will buffer the solution. Warmer water may have more dissolved minerals than colder water.

The temperature of the water is constant and always around 20 degrees Celsius.

I am using distilled water with a pH of 7,0 according to the label. Now, it is true that distilled water may react with the carbondioxide in the air, resulting with a slightly lower pH, but this is hardly significant. If your distilled water is not around 7,0 then it's probably not distilled water.

But the point is, even a PH meter calibrated in this way would not give such a spread without reason.
And the exact amplitue of the spread (which only can be determined with a properly calibrated pH meter, yes) is not important. The fact is that a spread exists, and the question is why.

u NEED 4.0 and 7.0 calibration or your meter will not read propply.also u need to buy some cleaner and sit the electrode thing in it for 10 mins

Right, well I'm broke so I can't buy buffert solutions or cleaners So that's not an option.

Would anyone care to guesstimate how many drops I should use? I'm gonna go with 7 drops unless someone has a better tip. The spread was big but with 7 drops the average pH was 6,2. Maybe someone has experience with dropping 38% nitric acid into 1,5l bottles of water? No?

Xschtar said:

Oh and by the way, the pH meter I am using is this one:
http://kinglead.en.made-in-china.com/offer/AoHnaCGOOfpe/Sell-pH-Meter-Model-PH-009-I-.html


View attachment 994379
I use my tap water as a reference to make sure it is calibrated, but I have also used distilled water. And yes, it is not a super-high quality pH meter and no, I don't have a real buffering solution - BUT, my pH meter gives correct and consistent results when testing fluids with known pH, so I have no reason to doubt it. And even if it's not 100% correct, it clearly shows that there is a great spread in my "pH-corrected" water and that, in turn, is consistent with the fact that I'm suffering from pH problems in my grow.

So it's not the meter and I can't for the life of me think that I'm distributing unequal amounts of pH-down, and I shake the bottle before use so the pH-down should be a homogenous liquid. What's left? Nothing!?

Click to expand...

thats a piece of shit meter. thats your problem. had that one before

I'll give you some advice from someone who did many similar experiments and spent waaaay to much time figuring it out.....Me!

I used to have a very similar PH meter. I knew my tap water was contantly running 7.4-7.6 and the distilled water I had said PH 7. I was using PH Up and PH Down (can't remember the brands but I tried a few).

Here's what I found....

The meter showed wide ranges of ph values with identical PH Up/Down doses. I couldn't figure it out. Even when using the water from the same distilled jug I received results that made no sense. I changed the battery in the meter, cleaned the meter and tried my experiments again. Again having almost identical results, I was perplexed. So I took some advice and ordered a Hanna meter (The nice $200+ kind) with PH/PPM/TDS/temp all built in. Since that very day, I have had no odd readings and things have become much simpler. I also changed to Advanced Nutrients PH Up/Down as well because it only take a couple drops vs dozens with other brands. I can also tell you my tap water does vary in PH from what I thought it was at with the other meter.

I know you don't believe it's the PH Meter, and neither did I. But once I got a nice one with some PH 7 buffer solution, I've have had no problems. And I was even having the same orange rust spots on my leaves that you posted in another thread. Not anymore!

Are you checking PPM or TDS?

Knowing that you said you can't afford a new meter or cleaning solution, I'm not sure how you are going to get consistent results or be able to diagnose problems. It's a must have for anyone expecting to grow healthy marijuana. You may want to get one of those $15 soil PH probes. I'm not sure how well they work, but it might be worth a shot. I've seen them at most stores like igrowhydro.com and bghydro.com. After all it's the soil PH we are really worried about isn't it?

That's all I can offer and I hope it helps. Good luck!

Xschtar said:

The temperature of the water is constant and always around 20 degrees Celsius.

I am using distilled water with a pH of 7,0 according to the label. Now, it is true that distilled water may react with the carbondioxide in the air, resulting with a slightly lower pH, but this is hardly significant. If your distilled water is not around 7,0 then it's probably not distilled water.

But the point is, even a PH meter calibrated in this way would not give such a spread without reason.
And the exact amplitue of the spread (which only can be determined with a properly calibrated pH meter, yes) is not important. The fact is that a spread exists, and the question is why.

Click to expand...

You never addressed how long you are leaving the PH meter in the solution before being sure about your reading. It can take several minutes for the PH pen to stabilize the reading so you may be taking it too early. If you are sure that you are carrying out the experiment the exact same way every time then it is the PH meter or calibration.

Go ahead and guess but at that point I would just throw out the PH meter as it is not going to help you at all. Sorry.

its crucial with cheap meters that u have both 4.0 and 7.0 if u have just the 7.0 your lower scale isnt so good

o and i found when swirling the ph pen in the water mine wouldnt sit still i had to keep the still for a good minute or 2 for an accurate readin

First off, distilled water is ALWAYS 7.0 pH. Otherwise, it's not distilled water. Secondly, I also believe your meter is the problem. Thirdly, many years ago I had a meter that took several minutes to stabilize and give me an accurate pH reading. It was a piece of crap made by Oakton over 12 years ago. I bought a replacement probe thinking that was the problem, but the new probe did the exact same thing. I currently use a pretty typical pH tester- the Oakton ph Testr2 (the green one), and have had no problems with it or its accuracy. Just to be safe, and in case something goes wrong inside it's little brain, I always have GH's liquid tester unit with the vial and drops on hand for redundancy.

Thanks for your input closed4fishing! It's interesting that you experienced the same odd results as I've just witnessed. A question for you: You said you experienced the same orange rust spots on the leaves. Was this because of too high pH? And if so, how much was is off by? And these odd readings you were getting, were they as spread as mine are? When you got your new pH meter, how did the "old" values relate to the "new" values - i.e. how much was the "bad" pH meter off by? Was is even in the ballpark? Now, I dont have $200, to be honest I dont even have $20, so do you have any advice for me to solve my situation using the tools at my disposal?

With regards to the time I let the pH meter probe sit in the water:
I always let the pH meter sit in water until the measured pH value has stabilized - i.e. it hasn't changed in 30 seconds. This usually takes a minute or two. I've found that it goes faster if you "stir" the water with the probe, like you would be stirring a cup of hot cocoa.

Thanks everyone for your kind replies. Unfortunately, I am a broke, unemployed student in a cold, inhospitable, northern European country just trying to grow some weed And no money for a pH meter! So if anyone out has any advice for me that DOESN'T include me purchasing new equipment, I would lick your toes for free! Or whatever you guys like.

I'm still gonna go with 7 drops in lack of something better...

Hi Xschtar. I believe the rust spots were because I had ph'd my water to what I thought was 6.6-6.8, but in reality with a new meter, I found I had been taking it down to 6.1 so. I believe it was Magnesium lockout. Heck, with the old meter, I wasn't even sure what was going on because sometimes I could get a nice 6.6-6.8 reading, then the next batch out of the same bucket would be down to 4.5ph. It made no sense especially since the nutrient amounts were so close and I used the same distilled water. The odd readings weren't quite as wide of a range as yours, but it was very close. Anytime your meter shows 2 full ph points of variation with the same water, something is wrong.

My suggestion since you don't have money for a nice meter is to get a $15-20 soil PH meter. You can keep using your PH meter to try and get the water as close as possible to 6.6. I'm under the impression that in the long run it's about the soil PH, so I'd focus on a cheap soil PH meter. I know it's going to be a pain trying to get it right, but I think you can do it.

One thing I have noticed in ph testing plain water is that reading can be unstable. Like when I use the ph pen to stir my water, the reading fluctuates greatly. My tap water is very pure where I live (rainwater tds 6 to 8 depending on season). However, when I mix up a batch of nutes (high tds levels), my readings are very stable. In fact stirring the solution doesn't even budge the reading.
This is just something I noticed. I use a Pinpoint ph probe by American Marine Inc. It was recomended to me when I used to have a saltwater reef aquarium. Ph was very important there too.