PH meter calibration

[Dwhitty76]

So, i recently threw away my ph meter paper strips because they sucked and bought a digital PH meter (PH-009 2 ATC).This is the first time i ever dealt with one.I followed the calibration instructions,which was to immerse the electrode into the PH 6.864 buffer solution and adjust the "trmmer"w/ a mini screwdriver untill the LED display read 6.86 and i did that.Then i immersed the electrode into the ph 4 buffer solution waited a minute like the instructions read, untill the LED read a PH 4 (it was automatically suppose to go down to ph#4),i wasnt suppose to have to tweek the trimmer to get the correct ph of 4.The ph only went down to 4.50's,so he tweeked the trimmer untill it read 4,then put it back into the 6.86 solution and it only raed 6.51.I re tweeked it till it read 6.86 then i soaked it in di water,just to make sure and dried it before putting it back in the ph4 solution and this time the LED read 4.36.So ultimately i calibrated it in the two solutions and got the 6.86 level but is only getting it down to 4.36 instead of 4.Is this a big deal? i want my Ph readings to be accurate,which is why i threw away the paper strips.Anyone know the answer?

 

[benzyme]

that's strange.. normally, these meters with ATC have automatically programmed calibration (you put it in buffer solution, and the computer adjusts automatically to match the pH of the solution). I have a Hanna with two-point calibration that displays "USE" when calibrating. if it gives an error, the electrode needs to be cleaned, or replaced altogether.

if you're unsure, perhaps take it back, discuss the issue with the dealer and request another meter.

rinse it with DI, but don't soak it in water that's been sitting out. water tends to pick up ambient CO2, making the water slightly acidic; these instruments are highly sensitive to electric potential, even static discharge from clothing. keep that in mind as well

 

[Dwhitty76]

yeah, i'll try again.The istructions said to tweek trimmer for the 6.86 buffer but not the 4 (it was suppose to go there automatically).You think i should but the electrode in di water and dry before butting it in the 2nd buffer or should i be able to just take out of one buffer and go srtaight to the other buffer w/out cleaning and drying.I'll try another time and then call the manufacturer

 

[Shaolin]

OK. I ordered "Digital pH Meter Tester Hydroponics Pen Aquarium Water" (similar to this one).

1. When I put it in distilled water (bought just an hour before) I got a reading of 8.2 but with every minute the number fell and after 15 minutes it was on 6.2 (and still falling). Why ?

2. I want to calibrate the meter. I've got those baggies with different pH buffers but I don't know how much powder to mix with how much water to get that desired pH. For instance it says "At 25C, 0.025M -> pH 6.86". All good but I don't know what kind of substance I have so 0.025 is pretty worthless data to me. How do I know how much to add ? Other writing is in Chinese so :S