Aquarium pH tests — on test!

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The pH kits in our tests were used in a variety of situations — some quite challenging.

We compare 20 aquarium pH test kits with prices ranging from £5.99 to over £300. How do they measure up?


WORDS AND PHOTOGRAPHY: GABOR HORVATH

Checking the pH of the aquarium water should be part of every fishkeeper’s weekly routine, as it could help to detect or avoid serious problems. There is an abundance of pH tests and meters on the market, but not all are equally reliable in every condition — results can be influenced by temperature, ionic strength of the water and by the pH levels you want to measure.


Can you trust your readings?

Having a correct buffering capacity is an essential factor in maintaining a steady pH. Fortunately it can be easily measured by a KH (carbonate hardness) test and adjusted if required. At close to neutral pH and at relatively high KH most of the tests here will give you quite reliable — and similar — values. But as soon as you move towards lower pH values, especially if paired with low carbonate concentration the results will be more scattered. Let me explain it through an example.

Think about pH as a noise and the pH tests as microphones. To be able to record the noise it has to be loud enough, or at least louder than the noise the microphone itself makes (I will come back to it later). The dissolved material content of the water — also called ionic strength — acts as an amplifier, making the signal stronger. Low KH water has low ionic strength, therefore you need more sensitive ‘microphones’. The problem is that the test liquids — being solutions — have their own ionic strengths, therefore if the external signal is lower than the internal ‘noise’, then there will be no reaction and no colour change at all. I found this particularly prominent in the case of broad range pH liquids. The same applies to the pH probes: most work fine in ‘normal’ conditions, but a few struggle at low KH.

How we tested

With the wide range of creatures with very varied requirements, that I keep, I was able to test these products in different — and sometimes quite challenging — situations. I tried to cover the most commonly used pH ranges as well as some of the extremes. Among the tested aquariums I had acidic, low ionic strength ones as well as alkaline tanks with high KH content. However, my tests were limited to freshwater only.  

Before the tests I calibrated all the pH meters according to the manufacturers’ instructions and made sure they had new batteries. To get the final results I repeated the measurements three times in every tank and — if necessary — averaged the readings. From the results table we can see that at the ‘normal’ pH 6.4–7.6 range most of the methods gave suitably accurate results.
This is good news, as it means you can choose almost any brand or product if your water falls into this band. At a higher pH there were some differences, but it was the acidic water that really tested the tests (pun intended). Even the broad range liquids struggled to give even near correct readings. So, if you need to accurately measure low pH it seems that a reliable pH pen or monitor would be your best option.

3 types of test kit

Liquid tests
These are probably the most well known and are based on the colour change of the indicator caused by the level of hydrogen ion concentration of the water. The resulting colour is then compared to a standard colour chart corresponding to a known pH. Some of the drop tests can measure a broad pH range (e.g. 3–10 or 4–10), but I found them quite inaccurate in acidic conditions. You could get better results with tests in the range 6–7.6 or 7.4–9.

Dip tests
These can give you a quick, albeit often less accurate result. Just dip the test strip in the water and match the colour on the reference chart or use your camera phone to take the readings for you. The test strips are sensitive to high humidity and can age quickly, so always keep the tub closed.

 

Electronic tests
Using a handheld or built-in electronic pH meters eliminates the use of indicators and also gives you an option to quickly check the pH in several tanks or monitor it in a permanent way. The most frequently used probes have a glass electrode and a reference electrode. They determine the pH of the water by measuring the voltage (potential) between them. The results strongly depend on the sensitivity and the quality of the probe, so it’s worth investing a bit more in a reliable meter to ensure you have accurate results. Some will even control and maintain the pre-set pH for you. Another issue that can have a strong influence on accuracy is calibration. Electronic pH probes must be calibrated regularly. The cheaper versions use only a one-point calibration (at pH7), but the better ones have two- or three-point (at pH4, pH7 and pH10) calibration. Check the manual as to whether your probe requires dry or wet storage, as the dried out electrode will deliver false results.

Best buys

Liquid tests
The broad range pH tests are like ‘one size fits all’ t-shirts: they cover most people’s basic needs but will only really fit a few. If you believe that you can’t live without such a test, then the TetraTest pH seems to be the most reliable among them.

In a ‘normal’ community tank you would be better off with one of the pH6–7.6 tests. They all returned good results and there was nothing to separate them in terms of reliability. Based simply on cost per measurement the API test is the most economical, so this is my best buy
in this category.

For the basic end of the pH scale I have only tested the JBL 7.4–9 indicator, which I received as part of the JBL Testlab set. It is, however, also available to purchase separately and is a must for alkaline fish.

Dip tests
The paper dip tests are suitable for quick indicative results. Out of the three tested brands I would pick the JBL ProScan, as it was accurate enough and also measures several other parameters. I gave it a win over the Tetra test because the ProScan will allow you to retake your readings (I found that the second reading after ten seconds gives you more accurate results) while with the Tetra app you would need to redo the whole test.

pH pens
Among the pH pens one emerged as a clear winner. It is the product I was most impressed with. The DTK PH-1 proved to be quite fast and accurate, and even its price is affordable — a very useful addition to the fishkeeper’s toolbox.

pH computers
The pH computers in the test had excellent build quality and seemed equally fit for purpose. The only significant difference is the appearance: the AquaMedic pH computer has an industrial feel with its rugged design, while the white touch-screen display of the JBL ProFlora pH Control Touch would look right even in modern homes. Therefore my best buy goes to the JBL ProFlora pH Control Touch.