accuracy of the PH meter

[five]

I have a reservoir(actually just a small tub) to prepare the water for my apistogramma tanks. I utilise the PH monitor to monitor the PH. This monitor has a probe which I place in the reservoir permanently. It gives PH readings of around 5 usually.

Lately, I got a new PH pen and got it calibrated. Used it to test the PH in the reservoir. Surprisingly, it give a different reading, which is 6.3. This I see it as quite a big different from that of the PH monitor. Initial thought is that I will need to recalibrate the probe of the PH monitor. That's what I did. Upon doing that, I find there's no problem witht he PH monitor, it's as accurate as it should be. By-the-way, the PH monitor is pretty new too.

So what's the problem? Both PH pen and PH monitor are calibrated using the same solution, but they gives different reading, a different of about 1.3.

Which should I trust? sigh....

 

[tjudy]

The pens, depending upon make and model, are the most likely to be inaccurate. However, the problem might be the sensor on the monitir probe. They do not last forever, and it is best to store them is a low pH storage solution when not in use. 5.0 pH is not as low as the storage solutions I use (4.01). Maybe leaving the probe in the vat shortened the life of the electrode? Just an idea....

 

[beleg]

True, the probes have limited life and its best to clean them every other week with acidic water (Ph 4 buffer solution).

 

[five]

Alright guys, thanks for the information. Maybe I should just put in more effort in maintenance.:wink:

But on 2nd thoughts, both are new, about a month old. They should be working fine, shouldn't they. The PH pen is from Hanna Instrument while the PH monitor is some Taiwan import, some brand like PH-999.

 

[RiC]

I got very bad results with those from Hanna instruments, I switched to Aquarium Marine years ago and I really prefer those

 

[tjudy]

I have had many years of very dependable service from a Hanna Combo meter, but I have recently replaced it with two new meters from HM Digital that are less expensive to purchase and have a unique feature that combines automatic one point calibration 'in the ballpark' with manual calibration to the specific value of the callibration solution.

 

[Apistomaster]

Hi Ted,
I would like to pick your brain about your thoughts on the combo-meters that test pH/TDS-conductivity. I wasn't sure if you were already referring to a similar one above because there are various combination meters available that measure different parameters.
I have gone 40 years getting by without an electronic meter but having
finally getting a RO/DI filter I have been thinking about the convenience of having a combo-meter.
I raise enough fish with different requirements that chemical kits can be time consuming. I have the time but not always the patience required to perform a battery of tests.
Larry

 

[tjudy]

The combo meter is nothing tricky, it has both a pH electrode and the TDS/conductivity sensors on the same meter. There is not a piece of technology I know of (such as a single electrode) that can measure both parameters. That being said, a pH electrode will not last forever, which means that when you stich a combo meter into a tank to measure the TDS you are shortening the life of the pH electrode w/o taking a reading... the meter is measuring the pH regardless.

The cost of a Hanna Combo meter is appriximately equal to buying the Hanna pH and TDS meters of the same quality, so there is not a financial advantage either. I like my combo meter because it is accurate, reliable and easy to use.

I have switched to the HM Digital meters (one for pH and one for TDS) because they are good meters and the company has provided them for one of the workshops that I do for aquarium clubs. After using them, I find that they have some features that I like, and they are as accurate and as reliable as the Hanna meter. Their price is better also. Through SpectraPure the pH meter costs about $65 and the TDS meter costs about $35, so the total price for both is $100. The Hanna Combo meter has a MSRP of $144, though it can be purchased for less (usually about $125), but still more than the HM Digital meters.

If you are new to using RO/DI, and want to be very specific about reconstituting rather than just making the water 'softer', I think that a good set of meters is essential. For most hobbyists just being able to cut the tap TDS by a certain percentage is enough. I am probably anal retentive about it... but hey... its my hobby, and I enjoy the water chemistry part of the equation. :wink:

 

[Apistomaster]

Hi Ted,
Thanks for the info. I like the ease of merely mixing RO with tapwater but there are some fish projects where it seems best to go to the extra trouble of formulating a closer simulation of their natural water.
Fortunantely those are the minority of fish.
I am trying to raise Coral Red Pencilfish and Dicrossus filamentosus which are more demanding than most when it comes to breeding.

 

[beleg]

Ted,
I have a pen pH meter and i plan to buy a tds meter as well. You have recommended HM , so i have surfed their website. They have several products in the range starting form TDS EZ to the TDS & EC meter Combo-100.. The combo meter is 60$ while the TDS4 around 35-40. For an apisto breeder does the extra investment for a combo EC&TDS meter worth it? i know the price difference is not much but i usually avoid spending money on unused features.

What is the expected lifetime for the units?