Trouble Calibrating pH Pen

[watts]

I have a Milwaukee pH51 pen. It's blue. I always store the pen in storage solution.


I put the pen in 7.0 calibration solution and adjusted the "7" screw until it read 7.0. No problem there. So then I rinsed it with tap water and put it in 4.0 solution and the meter reads 6.5 and no matter how many times i turn the "4" screw or what direction, it doesn't read below 6.4 pH in 4.0 solution.

Any suggestions?

 

[Hammerhead]

its gone bad... you need 2 cal points.. if one is bad you wont get a good reading.. Time for a new one.. I bought a good one that I can remove the probe when it get bad and replace it.. I also got a cheap one for emergency's

 

[watts]

thanks hammer

I can replace the probe for $45 or get a whole brand new unit for $50.. Not sure if i want to buy this same one again or not. It was only 12-18 months old.

 

[Hammerhead]

save your money and buy a Bluelab combo meter. There expensive but worth it IMO. It's no toy lab grade meter IMO.

http://compare.ebay.com/like/380324486079?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

 

[watts]

yeah that's a great meter i hear. How often do you suppose to calibrate meters? I never calibrated it much so I wonder if that has messed it up. Any info on how to clean the probe. I have some distilled white vinegar. Should I try soaking it in that overnight or rubbing alcohol?

 

[Hammerhead]

only when you need to... If you suspect the readings your getting are bad cal the unit...

NEVER USE RO water to store your probe... The storage solution should have a ph of 4.

Here is all the info you need

http://www.coleparmer.com/TechLibraryArticle/1189

 

[TribalSeeds]

Try replacing the batteries first. Its good to have backup batteries and strips or another pen on hand.

 

[growshopfrank]

Try replacing the batteries first. Its good to have backup batteries and strips or another pen on hand.

this is good advise also there is a cleaning solution for ph pen electrodes
http://www.hannacan.com/conseils_pH_en.htm

FWIW 12 to 18 months life isn't bad at all for a ph pen