# Help me choose a pH meter



## Sacha (18 Nov 2014)

I want an accurate pH meter/ pen so that I can carry out proper pH profiles. 
I am looking at the Hanna ones and I have narrowed it down to these two: 

http://shop.hannainst.com/hi98103-checker-ph-tester.html?id=040003&ProdCode=HI%2098103

http://shop.hannainst.com/hi98107-phep-ph-tester.html?id=033001&ProdCode=HI%2098107

The first one has a resolution of 0.01, but an accuracy of +/- 0.2. The second one has a resolution of 0.1, but an accuracy of +/- 0.1. 

So, does this mean the second one will give me more reliable, but less precise readings? Does the fact that the first one has a separate probe mean that it will be less likely to become inaccurate over time? 

Why is the second one more expensive? 

Cheers.


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## Sacha (19 Nov 2014)

No-one?


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## GlassWalker (19 Nov 2014)

Only speculation, but maybe the electronics in the 2nd are better designed to be more stable and reliable, thus giving the tighter accuracy claim.

At a practical level, both feature 2 point calibration so that's good. Beyond that, I think is over-analysing. Do you need 0.01 resolution? I have meters that do that, and I just find myself obsessing over the last point even when I know the difference in practice is irrelevant.


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## RossMartin (19 Nov 2014)

I use an Atlas Scientific one plugged into my Raspberry Pi to plot my ph!!


Sent from my iPhone using Tapatalk


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## RossMartin (19 Nov 2014)

I use an Atlas Scientific one plugged into my Raspberry Pi to plot my ph!!


Sent from my iPhone using Tapatalk


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## Sacha (19 Nov 2014)

Ok, let me add that I am not wanting to spend more than about £30 here. 

GW, I do not need 0.01 resolution. So then you reckon I should get the pen? Are meters that have an external probe (the first one) more reliable than pens, which have the probe built- in?


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## GlassWalker (19 Nov 2014)

According to the link you provided in the 1st post, even the pen one has a replaceable probe (junction). So if it needs to be replaced later, there is still that possibility. I suspect as long as the calibration is performed correctly, preferably around the same temperature as the tank would be, the results of either will be good enough.


Edit: thinking more, I think calibration solutions are usually specified for a given temperature, maybe with compensation at other temperatures. But again for aquaria, the differences are pretty small.


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## LukeDaly (3 Jan 2015)

RossMartin said:


> I use an Atlas Scientific one plugged into my Raspberry Pi to plot my ph!!



Hopefully you have a tutorial or guide on this somewhere? Got 2 Pi's from previous projects sitting here. 
How accurate is this? 

Thanks, 
Luke.


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## RossMartin (3 Jan 2015)

Hi Luke,

No tutorial yet as i'm still playig but if you go to pi.plantedpi.co.uk  you can see what i have been doing. If you are a geek like me you can go to http://pi.plantedpi.co.uk/index.php where i am createing a Star Trek theme (this is for another project i am working on!). The webistes are created using PHP and JQuery. The monitoring scripts that the Pi uses are done in Python.

Both pages and the projects in general are works in progress so the webpages and the coding isn't anywhere near finisehd yet!

The Pi will monitor PH, in Tank Temp and Flow and then plot the graph. You can change the graph timescale using the drop down boxes. I also have a second temperature probe and a humidity sensor however this only shows on the Star Trek themed page!

The flow meter is installed, however i was getting some varied results so i have coded it to just add 600lph everytime the data is logged which i think is every five minutes. (this will change ten minutes at some point).

The PH meter appears to be very accurate, however i only have a cheap £10 meter off ebay to compare it to!

Cheers

Ross


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## dw1305 (3 Jan 2015)

Hi all, 
I haven't used either of them, but Hanna is a good brand and I'd probably go for the second model. Two point calibration is what you need, but you need to calibrate the meter *before every use, *using both the pH4 and pH7 calibration buffers*. * If you use EI your tank water will have a reasonably high conductivity, which will stabilise the pH reading.  

We have a lot of "cheap" pH meter ranging from ~£200 to ~£2000, and they are quite high maintenance bits of kit. Buffering the meter before every use seems a fiddle, but if you don't do it the values you get won't be reliable readings. 

You also need to store the meter with the electrode in the correct storage solution, the technical sheet should tell you what it is (depends on the electrode, it may be one of the buffers or KCl solution).  

cheers Darrel


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## pepedopolous (3 Jan 2015)

How unreliable can the readings be if you don't do the things you said?

My meter measures to 2 decimal places and CO2 makes the pH decrease as expected. The electrode sits permanently in the aquarium water and I calibrated it (2 point) some time in the past month.

P


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## RossMartin (3 Jan 2015)

The sensor uses a 3 point calibration...according to the manual it can be done once a year....however i'm not sure that is good enough! What i have done is taken a reading, done a calibration and then taken a reading again and they do appear to be identical.

Here are some photos or the Pi circuit and the sensors in the tank.


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## dw1305 (3 Jan 2015)

Hi all,





pepedopolous said:


> How unreliable can the readings be if you don't do the things you said? My meter measures to 2 decimal places and CO2 makes the pH decrease as expected. The electrode sits permanently in the aquarium water and I calibrated it (2 point) some time in the past month.


It is going to depend on the type of electrode. If it is a solid state <"ISFET"> meter designed for long term immersion it is probably OK. If it is a glass electrode, until the electrode fails it will give you a ball park figure, with certain proviso's. 

The problem for all pH measurement is the pH scale itself, because it is a log10 ratio it works very well in highly buffered acid, or alkaline, solutions, but around pH7 (10-7 H+ & OH- ions) or in solution with few ions, it is a moveable feast. This leads to one of the other problems with pH,  it needs some interpretation.

Another problem for all pH meter is the <"reference electrode"> which works by continually leaking KCl solution. Some electrodes are re-fillable, but most are single use only.

cheers Darrel


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## Carl Whitbread (3 Jan 2015)

Sacha said:


> Ok, let me add that I am not wanting to spend more than about £30 here.



I have a Seneye Home. It is brilliant and it is so simple to use. Albiet you do have to buy slides (£18 for a 3 month supply) but it will send you a text and an email if there is a problem. It also measures temperature and Ammonia as well as light. You can buy the device for about £30 second hand off ebay. I have an old PC that mine is plugged into so I get 24 hour monitoring. I have used this device for about 2 years now and cant fault it and the support team are excellent. It has really saved my fish on at least two occasions. Anyway, good luck with what ever you decide to buy but perhaps review Seneye on Youtube unless you have already bought something by now as I see this post is a couple of months old - it was just my imput.

PS - I do not work for Seneye.. I just love the product


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## Sacha (3 Jan 2015)

I have a Seneye Home. Don't get me started on it, but the slides are incapable of measuring pH in water with KH less than 5. 

They have been promising a "low pH slide" for over 2 years now, but it never materialises.  

My Seneye Home is just an expensive thermometer. It can't measure pH in soft water. 

They don't tell you that either, they let you work it out yourself.


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## Sacha (3 Jan 2015)

http://www.ukaps.org/forum/threads/seneye.31700/

Read through that thread


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## pepedopolous (3 Jan 2015)

Seneye can't measure pH less than 6.4. Only found out after I bought one. Useless for me. Possibly an OK PAR meter but I doubt it.

P


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## Carl Whitbread (3 Jan 2015)

pepedopolous said:


> Seneye can't measure pH less than 6.4. Only found out after I bought one. Useless for me. Possibly an OK PAR meter but I doubt it.
> 
> P


That is very true. But with the Seneye Web Server now on the market Seneye told me that it will have future capabilities... What did they mean by that statement not sure but watch and wait to see what happens.


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## Carl Whitbread (3 Jan 2015)

Sacha said:


> http://www.ukaps.org/forum/threads/seneye.31700/
> 
> Read through that thread


Sorry to hear about your experience Sacha and thank you for the link to the post - Gosh what an eye opener. I have very hard water and the published PH from my water supplier is 7.30 but my seneye reads my tank PH as 7.15 - I put this down to some of the PH changing as it is pumped from the water supplier as they have said on their website that this may be the case. I have in the past used RO water and the Seneye was very good at providing me with PH moniotring so I could see the PH swings - but now I ask how accurate where those PH readings after all?
I use to have an API test kit but went away from it as I was sold on the idea of better accuracy and realtime monitoring. I don't feel duped just a little concerned. I don't want to go back to liquid test kits but I am tempted now. Sadly, I have just bought 6 months worth of slides, I suppose I could sell it as a job lot. I was also tempted with a PH meter but read bad reviews about them too. I suppose there are always pros and cons to everything. All I can say about my Seneye is that £80 a year to monitor my aquarium was always a price I was prepare to pay but as for now - well I 'm not so sure if I want to keep it


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## Sacha (3 Jan 2015)

I never paid for the slides. 

A slide will accurately measure pH and ammonia for well over a month. The slides can be used for about 3-4 months without any loss of accuracy. 

The only thing you don't get are the text notifications, but you don't need those anyway if you install the Seneye app.


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## jaypeecee (21 Jan 2015)

I have been using a seneye monitor for over six months. My tank water is 4.5 - 5.0dKH and GH is 8 degrees. The seneye consistently reads high on pH. I have checked it against an Extech PH100 pH meter (freshly calibrated using buffer solutions). When the seneye was reading 7.42, the Extech reads 7.10. That's quite an error. I do not understand the relevance of the graph on the seneye website talking about ionic strength. Starting with RO water, I make up the water in my tank to a conductivity of around 400uS/cm. Besides which, the seneye does not rely on ionic strength as it uses an optical system for measuring pH.


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## GlassWalker (21 Jan 2015)

While the reading may be optical, it is reading the colour change on some chemical reactant on the slide. Presumably if the "ionic strength" gets too low, there is insufficient reaction to give a proper colour change and therefore reading.


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## jaypeecee (22 Jan 2015)

GlassWalker said:


> While the reading may be optical, it is reading the colour change on some chemical reactant on the slide. Presumably if the "ionic strength" gets too low, there is insufficient reaction to give a proper colour change and therefore reading.



Hi GW,

Yes, you have a valid point. Although there is a good deal of material on the Net about electronic colorimetric methods, I have not been able to ascertain the accuracy of these methods. But, I haven't given up looking.

JPC


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