Strange results re-calibrating pH pen

[Hen]

TLDR; I re-calibrated my pH pen. The pH pen reported the 6.86 calibration solution I prepared was the same pH as my mains water, 8.3. Has this happened to you before? What do you advise?


...So I picked up a cheap pH pen from China which IMO worked great. First time calibration with the included calibration packets was nearly spot on. Testing the pH my water reported exactly what the water company stated it was.

During the last 5 months I've been keeping it in the 4.0 solution between measurements. Using it has been great, but I decided it was time to re-calibrate again (like you are supposed to do, apparently). I ordered the same packets again, but this time from a different online seller because the original seller didn't sell just the calibration packets. They looked identical -- 6.86 and 4.0 packets. I followed the same steps as last time, getting the water to 25C and dissolving each the packet into 250ml water. When I tested the 6.86 solution, nothing! It had no effect on the original pH of my mains water. I didn't know what to do.

Do I ignore the whole thing and stop right there? Or could this be normal. I mean, how could a packet of crystals do nothing? Did they fill it with sugar or something!? Do I turned the screw down and down until it reached 6.86. Then I tried the 4.0 packet. This was a little better as it wasn't too far off, so I adjusted it as instructed. When I tested my mains water again, it was way off from the specified pH. I guess I fucked up.

Do you think this is a problem with the pH pen, or with the 6.86 calibration packet?

 

[PetFlora]

tips do go bad. If yours is replaceable try that, or just get a new pen

 

[chris harris]

I'd go to hydro store and buy a bottle of 7.0 calibration solution. You gonna need it anyways as you should be calibrating that pen on a regular basis. If your pen don't calibrate properly, then probe is probably bad. Mixing powder sounds like a hassle, but if that works for you, buy a bunch of packs.

 

[Cadfael]

Do not keep your pen in a 4.0 solution. They are meant to be kept in water. That will decrease the life of your pH pen.

I agree with chris Harris. Buy the GH buffer solutions (7.0 and 4.0) and use those. At 8 USD per 8 oz(?) each it will last you a long time.

I would calibrate at the first of every month. Makes it easier to do it regularly.

I would also recommend a pen that reads to only a .1 variance. you do not need a .01. It is not needed, is more expensive, takes to long for for your reading to calm down, and is more of a PITA when calibrating.

 

[RB56]

Are you dissolving the crystals in tap water? That doesn't sound right. Get the premixed solutions. You also want to store your probe in storage solution or untreated tap water, never distilled or RO water. Suggest you also pick up some pH testing drops. Only a few dollars and you'll have both a reference and backup. Not having confidence in the pH of your solutions is a recipe for problems.

 

[gaiusmarius]

yes indeed, buy buffering liquid at the specified readings of your instruction manual. most ph pens are calibrated with ph 4.0 and ph 7.0 buffering liquid. why are you talking about 6.86? is that what the pen calibrates at?

as was said crystals in tap water won't be leliable as the tap ph will screw it up. maybe with distiled water, but the premade solution is best imo.

once you get the calibrating liquids, do the whole thing again. get back to us how it went.

 

[BOMBAYCAT]

PH pens/tips do wear out (bad readings) after time. I buy the cheap pens and get about 3 years out of them. When the pens start getting slow to change the reading I know it is time for a new one. I use 7.0 calibration solution for storage also and re calibrate monthly I guess.

 

[gaiusmarius]

there is a special liquid called kcl liquid which is supposed to be great for ph sensor storage. to be honest the cheap pens seems to get by without needing this liquid. i just calibrate every year or so, unless something fishy happens when i'm using it. some times things give you reason to doubt. specially once you are dialed in with your water and how much it measures in various situations, so i would notice right away if my pen goes off.

 

[Hen]

Sorry folks, I've had a busy week and just got a chance to sit down at the weekend and check my email.

The calibration packets in question were

I should checkout what they have at the local grow shop. Calibration fluids sound better and I think the instructions on the pen packet said to use distilled water, but it's seriously hard to get things like that where I live.

I might also put in an order for a new pen.

 

[chris harris]

While your at it, get small piece of foam, or cotton. Stuff some of it down in the cap, and wet it. That way when your done using your pen, and you put it away, the tip don't dry out.
You can buy storage solution for your pen as well.

 

[gaiusmarius]

you can get distilled water in any supermarket. it's used for car batteries too as well is irons.

the tap water has it's own ph, so the powder won't mix true if you use tap water.

 

[Mikell]

On the distilled or tap, think garbage in/garbage out.

It was my understanding KCL storage solution is also the liquid in the electrode tube, and a 24hr soak will correct gradual deviation.

Perhaps more relevant to wall mount units. Either way, it is preferable to verify calibration with drops or paper, all pH meters fail one day.