pH tester

jameson_uk

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I am after recommendations for a quick cheap pH tester. I had a generic pen from Amazon which seemed ok but only lasted 8 months before giving up working all together.

I do have an API kit but annoyingly my pH seems to be just in between the standard and high range tests and being colourblind it is always a pain to do these tests.

Am I right in thinking that pH is one of those things you can actually test reasonably accurately?

Are the cheaper pens fine? Or the paper tests that are sold as hot tub tests etc?

Any recommendations for a cheap test that I can use quickly and easily a few times a day.
 

dw1305

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Hi all,
Am I right in thinking that pH is one of those things you can actually test reasonably accurately?
You can, but usually in situations where you already have a good idea what the pH is likely to be. The problem is really that pH is a very strange measurement, it is both a log10 scale and a ratio.

If you have hard, salts rich, water then the pH will always be about pH8, and your pH meter will tell you that, the same applies to very soft water with added acids (even just CO2) you are going to be down at pH5 and any meter will tell you that.

The problems come when <"you want to measure between those extremes">. As an example this is the titration curve when you add hydrochloric acid (HCl) to sodium (bi)carbonate (NaHCO3/Na2CO3) solution. This one is very relevant to those who inject CO2.

carbtitrate.gif


Which is another way of showing the two stages of the TIC curve.
co2_hco3-png-1550-png.png
Are the cheaper pens fine? Or the paper tests that are sold as hot tub tests etc?
That is really back to your <"pH probe"> thread.

cheers Darrel
 

jameson_uk

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That is really back to your <"pH probe"> thread.

cheers Darrel

AHH yes. pH is too short a search term....

My output from that thread was a probe wouldn't last that long and there were issues doing it with a pi. I kind of skipped the bit about the issues with measuring it.

Now you have written it down it is obvious that pens would be no different to cheap probes (and probably more so). What about reagents and strips though? These obviously don't have the same issues as probes but I am guessing they still struggle measuring the range we are interested in.
 

jaypeecee

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dw1305

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Hi all,
AHH yes. pH is too short a search term...
I know, "CO2", "pH", "TIC", "NO3", "ion" are all too short to use as search terms. I cheat a little bit by adding "bromothymol", "NO3-" etc. to any CO2 etc. posts I make now, but it doesn't work for finding other people's posts, or for my older posts.
What about reagents and strips though? These obviously don't have the same issues as probes but I am guessing they still struggle measuring the range we are interested in.
Yes, you can use a <"narrow range pH indicator">, like the ones that @jaypeecee links in. The "JBL PROAQUATEST pH 6.0-7.6" I assume that uses bromothymol blue, like a drop checker would.

These are all forms of <"acid base titration">, and have the same issues with weak acid and bases.
.....Notice that there isn't any steep bit on this graph. Instead, there is just what is known as a "point of inflexion". That lack of a steep bit means that it is difficult to do a titration of a weak acid against a weak base......
wawb.gif

Did a quick search on amazon for it, seems to be more expensive:
That one would give you a ballpark figure, it really depends how much accuracy and precision you need. If you want something that is accurate and precise in low ionic strength solutions (like soft tank water) you would need a <"much more expensive meter">, which needs two point calibration every time you use it.

I don't often try and measure the pH of the tank water. If you dip a meter in you are really just measuring the <"dissolved oxygen : CO2 ratio">. I can get a more accurate reading by taking the sample away (in scrupulously cleaned glassware), adding some NaCl (a neutral salt to raise the ionic strength) and then calibrating and using three of the bench type pH meters linked above.

Alternatively I can observe the <"condition of the snail shells"> and <"measure the conductivity of the water"> with a dip meter. It doesn't sound as scientific but it gets you to the same place a lot quicker.

cheers Darrel
 
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For what we do as hobbyists aren’t PH papers good enough? Surely we’re only looking at a ballpark figure.
 

dw1305

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Hi all,
For what we do as hobbyists aren’t PH papers good enough? Surely we’re only looking at a ballpark figure.
I think for most us they probably are, the real issue is for CO2 users, where not knowing what the pH is can easily lead to asphyxiating all your fish.

cheers Darrel
 

ian_m

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You need to ask "Why do you need a pH value ?". What would you do different depending on your pH value ? How would you keep plants/fish differently depending on the unreliable pH value you got ?

I have both pH papers and drop test kit, never used in anger, other than to prove how difficult it is to get a meaningful reading. In fact both in the bin now as during a recent clear out of "stuff that I bought that I thought would be useful" they had expiry dates of Feb 2017. Must have got at least 5 years before that.

One place you can use a pH value, actually differential value, is using a pH pen to measure CO2 levels. 30ppm CO2 causes a drop of 1 pH, thus you can use a pH drop of 1 unit as an indicator you have got 30ppm CO2. Can't use a liquid or strip test as these are influenced by other ion/salts/chemicals in the tank water. Left over dechlorinator in fish water is a major contributor to inaccurate readings of test kits, especially nitrate and ammonia tests.
 

Sammy Islam

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I think it's more useful to rely on a calibrated ph pen than let's say BPS. Most people probably run uncountable BPS, especially with hard water and trying to achieve a "1 point drop". So measuring PH is generally more reliable than measuring BPS.

I also think it's main advantage is you can gage if you have consistent or fluctuating co2, regardless of the PH, that's the main reason i use mine.
 

Andy Thurston

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I hate the numbers:lol: drop checkers and any device used to test the amount of co2 in the tank. The most accurate method is watching livestock. Adding large amounts of co2 to a tank is a risky business but knowing your critters and how they behave will give you a much better indication of co2 levels than any piece of equipment you choose to stick in your tank
 
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