PH Pen Strange Results

[JohnH]

Along with my TDS Pen that arrived yesterday, I also got a PH Pen.

The PH Pen came with two packets of buffer to calibrate the pen. I did the high one yesterday and set it to 7.5 (I think that was the buffer). Anyway today I checked my cherry tank and it is telling me the PH is 8.5 :cower:

When I test with the API kit I get 7.6 using the normal PH test and 7.4 using the high range test.

So I break open the other buffer packet that came with the PH Pen (this one is 4.5). Wack the pen and it reads 4.5. :crushed:

Ok, so which one do I believe.

[BlueBolts]

The calibration solution is should either be PH 4, 7 and 10. Most pen calibrate the 4 & 7.

[JohnH]

Ahh, yes it is 4. I recalibrated the pen so it is a 4 in the buffer mix. But it still reads 8.0 in the tank compared to the 7.4-7.6 from the API kit.

[BlueBolts]

If you calibrated the pen with the 4 & 7, and then test the reading with the solution again (also test it against you RO water where it should read close to 0) and it reads 8, then I'll probably rely more on the pen then the APi test kit.

[JohnH]

Should RO water be 0 or 7?

Unfortunatley, I ditched the PH 7 test water last night so I can't retest that. I've kept to 4ph water in a jar for now.

[Squiggle]

RO water has a pretty unstable ph as there's nothing in it to buff the ph, I wouldn't think you could use it for calibration :encouragement:

[JohnH]

I tested my fresh batch or RO water and it read 7.0 on the pen after I calibrated it in the 4.0 solution so it must be fairly close. That would mean the API test kit is off a bit.

I've ordered some new 7.0 (6.89) PH buffer powder so I'll make sure I keep it in a jar for future calibrations instead of tossing it down the sink.

[BlueBolts]

Oops, I confused the conversation between TDS & PH.

We're talking PH, so ignore my RO water test statement ! Sorry for the confusion. :redface-new:

You really need at least 2 points to calibrate, so a 4 & 7 solutions is really required.

[JohnH]

No worries. I've never really worried too much abut ph, I just left it as it was. When I get the new powder I'll do another calibration.

[planted]

make sure you read the instructions and calibrate the unit in the order it tells you and how it tells you.

there are quite a few different pens on the market and they vary in how to calibrate them.

usually you will calibrate pH4 then it will ask you to do pH7, then enter and your calibrated.

also make sure the numbers stabilize before entering each calibration point.

the more expensive/better quality pens will have 3 point calibration IE : pH 4 - pH 7 - pH 10

you should also keep the probe wet at all times when not in use too, otherwise it can loose calibration very quickly and will need re-calibrating more often.

we sell a couple of good brands where i work and one particular brand had issues with calibration, IE : quite a few were faulty an just wouldn't calibrate accurate.

they were $200+ pens.