Newbie ORP User needs advice

[quatermass]

I've just bought myself a £20 ORP meter off ebay.

Unfortunately it comes with no calibration solution.

The seller tells me it is precalibrated and will not need recalibrated for several months.

So I dunked the end into my newest planted tank (only 3 weeks old) and it reads 165mV after 2 mins.

Some de-ionised water reads 126mV after 5 mins.

My scottish soft tap water is only 99mv.

I was of the opinion that a good redox value was 300mv!

As this is my 1st ORP meter can some wise person guide me?

Is it broken?

 

[Tom Barr]

Re: Newbie ORP User needs advice

Redox meters need to sit for awhile prior. Give them 30 min or more.
Also, any stray current will reduce the readings etc.

Regards,
Tom Barr

 

[quatermass]

Re: Newbie ORP User needs advice

Redox meters need to sit for awhile prior. Give them 30 min or more.
Also, any stray current will reduce the readings etc.

Regards,
Tom Barr

So best to put a sample of the water into a cup and leave it sitting for 30mins is what you're saying?

Goodness, didn't read that it took so long to do a test.
Thanks.

 

[Tom Barr]

Re: Newbie ORP User needs advice

It takes awhile to get steady readings often.
Stray current will mess with it, same with pH etc.
Turn lights off etc.

See how much drift it has.
Check with a calibration set up.
I use a calomel ref electrode for the Redox meters, that way it's always references when I take a reading, they ain't 20 pounds though

You might want a new probe for good keeping.
Not sure.

Regards,
Tom Barr

 

[pepetj]

I have a Hach Redox pocket meter. It cannot be calibrated but a reference solution can be used to figure out if readings are reliable or not. Keep in mind that Redox is not supposed to be a somewhat steady reading like pH since this parameter is constantly moving in one direction and then on the other; what I look for is for those variations to stay within certain range (e.g. -200mv to +200mV).

I take a sample of tank water and let the probe sit in it for at least 20 minutes. I continue doing other things (likely taking GH and KH readings or getting some coffee ready). I had no idea I had to turn lights off (wonder how that affects Redox potential) but I did notice that water current does affect readings. I rather take readings directly in the tank, looking for calm surface areas (which shouldn't be a problem in planted tanks).

There should be a way of making a DIY reference solution for ORP meters... then again it may be safer and easier to purchase one.

Pepetj
Santo Domingo