Avoid common mistakes when measuring with test strips and PROSCAN in the aquarium - Video tutorial
Test strips are a reliable and popular way of determining different parameters in human medicine or in the household. They’re done at the doctor's and by you at home. Whether it’s for blood sugar, cholesterol, the salt or chlorine content in the hotel pool, the hardness of your water for your washing machine or the pH value in your urine - their possible uses wide-ranging.
Quick tests in the form of a test strip are not only used in the professional and medical field, but also in aquaristics.
Aquaristics also have other methods. For example, the popular drop tests ( PROAQUATEST & náhr. bal. ). Alternatively, you can have a laboratory test or use dedicated measuring devices with sensors, such as the JBL PROFLORA CO2 pH SENSOR SET .
As stated in the our blog post Display Accuracy vs. Measuring Accuracy - Different Results When Measuring Temperatures , explaining temperature measurement, water tests also have a measurement accuracy and a display accuracy. The latter results from the scaling steps of the colour chart, used for comparison in drop tests and with test strips. The accuracy of such a test method is generally limited by our ability to distinguish between these finely gradated values with the human eye. For printed products, therefore, so-called densitometers are used, as they can distinguish even the finest nuances and compare them with a "template". The human eye can only do this to a limited extent. With the JBL drop tests, the human eye is backed up by the comparator block, which virtually disregards the influence of the incident light.
Test strip accuracy
"This is inaccurate" or "this is no good" – you’ll hear comments like this again and again in the aquaristic scene. However, the methods do give precise results. So where does this persistant rumour come from?
The scale points shown on the colour charts and the measurement accuracies of the respective methods show that accurate results are technically possible. And even if laboratory measurements do produce finer gradations, it’s by no means a given that an even more finely scaled result would lead to a different assessment of the situation at hand. Would a pH value of 6.95 lead to a different decision than that reached with a value of 7.0?
Within one minute the quick tests allow us to assess seven water parameters. We then know whether a value is just right, too high or too low. If there is a problem, it does not matter if the nitrite value is 0.5 mg/l or 0.65 mg/l. Both are wrong and require your action. If you still want to know more precisely, use the drop test ( JBL PROAQUATEST NO2 dusitany ).
Thus, with scaling, the results are congruent even when we receive two different figures. In maths lessons at school, we learned about rounding numbers up or down. This is exactly what happens in test procedures with different scaling.
Example: The scale points of the pH value for a test strip JBL PROSCAN run in steps of 0.2. 6.6-6.8-7.0 etc. The measuring accuracy is plus/minus one scale point. The pH sensor measures accurately in increments of 0.01, but displays in increments of 0.05. Thus, 6.85 is either 6.84 or 6.86. If the test strip reads 6.8, both results are the same. The assessment does not lead to a different result.
Now there is one more point. Provided you carry out the test and the reading correctly (below you will find a video and all the necessary instructions. If you take two separate measurements, the results for the pH value are 6.6 and 6.8. If we look at both results, they differ by only one scale point. What is the cause? Both the human eye and the app-based measurement assign the colour of the field on the test strip to exactly one result on the colour chart.
If the result is exactly between two scale points, for example 6.6 and 6.8, the result is assigned upwards or downwards (rounded). One measurement is 6.65 and the other 6.75. Thus, 6.6 may appear once and 6.8 once. Don't be put off by this, both are correct and do not lead to any other decision. If you have paid attention correctly, both results were also different in the background. This is usually due to small errors in the application. You will find these explained below in the video and in the following text.
Even if a digital measurement suggests that it is in 0.0001 increments, a digital measurement needs fixed scale points. These are chosen so "robustly" that minor inaccuracies in the application cannot lead to jumping and changing results. Only the value between two scale points causes the aforementioned uncertainty.
The digital test strip with app
I’m sure you already know that test strips are a simple way to check the water quality. On the test strips there are small square fields that react when they come into contact with water and reagents on the strip cause these to undergo a colour change. This is compared visually, i.e. by eye, with a colour comparison card and the correct pair of values is determined.
The accuracy of reading quality can be affected by the individual user’s eyesight, by the ambient light or by damage to the colour card caused by water or fading in the sun. With the digital version JBL PROSCAN , the accuracy comes from the interaction between your smartphone camera, the JBL PROSCAN App and the JBL ProScan ColorCard in credit card format. The application works in the same way. The app guides you through the correct application and allows you to scan the test strip on the ColorCard once the 60 second wait has expired. The ColorCatcher technology in the background does the rest automatically.
Light, visual impairment, colour blindness or ambient light are recorded with colour accuracy and interpreted in interaction with the reference fields on the ColorCard and the results of the analysis parameters are determined. The result is an objective, digital evaluation that is more reliable and accurate than an evaluation by eye. The stored value ranges are on average twice as finely scaled as the possible scale points in analogue measurement. Together with a ColorCard, which has been tested for colour accurancy, the test strips are packed in smaller container sizes especially for PROSCAN. The anti-moisture cushion contained in the head of the tube continues to ensure good quality for several months after opening.
Avoiding measurement errors - A list of typical application errors
Above I described how the measurement and display accuracy of test strips provides reliable and accurate results. This of course assumes that you perform the test correctly and do not make any mistakes. Even in the laboratory, mistakes in the evaluation would lead to wrong results. You now have your mini-laboratory to hand and can expect accurate results with very little effort.
When we received reports of unreliable and incorrect values and looked at the test strips on the ColorCard or colour comparison card afterwards, there were always errors in the application of the test or the reading. This realisation convinced us to make this video available to you. Here you can see how a measurement is carried out correctly and which application techniques inevitably lead to deviating values or even an error.
We have compiled the points shown in the video for you again in writing:
- Lay out all the parts you need.
- Make sure you have an ideal recording location in uniformly bright, natural light.
- Place the JBL PROSCAN ColorCard on a matt, non-reflective surface that can absorb water.
- A sheet of kitchen roll or a paper handkerchief is ideal for this.
- Remove everything you do not need from your work surface.
- Start the app and read the instructions.
- Start the timer.
- Immerse the test strip in the aquarium water for 3 seconds.
- Remove the test strip from the water.
- DO NOT shake the test strip, but tap it sideways on the absorbant underlay so that excess water is removed and the fields do not react with each other.
- Place the test strip on the ColorCard.
- After the timer of 60 seconds has expired, align your smartphone (within 3 seconds) directly parallel (horizontally) to the ColorCard so that it is completely in the picture and only a few millimetres remain free at the edges. The scan starts automatically, 3 seconds after the timer has expired. It can be triggered by pressing the display again as "focus" if the scan was not successful.
- Now you can read the results of your current measurement and view the recommendations.
- Now switch to Analyses and view your most recent measurement in comparison to your previous measurements.
1st Source of error: The surface
Having an unsuitable underlay or no underlay at all can deceive the digital eye of your smartphone camera. Reflections of light from a reflective surface, puddles of water or a non-horizontal orientation of the smartphone to the ColorCard (namely holding the smartphone diagonally or sideways in front of you) can cause such problems. Glass or smooth surfaces are a particular problem.
A sheet of kitchen paper or a paper handkerchief is an appropriate underlay as it not only absorbs the water but avoids reflections.
2nd source of error: Use of the test strip
The test strips react once to contact with water. This means that it’s important they were dry beforehand and that they can only be used once. So never leave the tube open, pour out the test strips or touch the fields. Splashes in the tube will render the strips unusable. Errors caused this way often manifest themselves as chlorine values that are not present in the water.
Each of the small fields is a separate test. So don’t just shake the test strip once it has been taken out of the water. This will cause water from one field to enter the next. Cross-reactions will occur. Moreover, shaking the test strip in the air means not enough excess water will be removed. Water bridges will form between the fields. These not only irritate the digital eye, but also falsify the reactions of the test fields. This often manifests itself in differently coloured edges.
After removing the test strip from the water, guide it directly to the underlay and tap it (gently) sideways on it. This will remove the excess water without cross-reactions occurring.
3rd source of error: The lighting
You’ll have the best conditions in a room with good natural light. Very direct lighting at close range creates partial shadows on the ColorCard, which, however, needs to be evenly illuminated. That’s why you also need to deactivate your flash light, as this would also cause reflections. Artificial light or even strong coloured light from an LED can influence the test. Insufficient illumination causes ISO noise and weakens the reference value reading. Measurements at the aquarium or under a desk lamp are therefore not reliable.
Take the test near the window or in a well-lit room.
4th source of error: The ColorCard
The scanning process covers all the colour reference fields of the PROSCAN ColorCard, taking into account your camera data and the ambient lighting, and compares them with the colour fields of the test strip. For an accurate result, the ColorCard must not be damaged by scratches, water stains or bleached spots (storage in the sun).
Store the ColorCard in a dark and dry place in the aquarium cabinet.
5th source of error: The scanning process
It is important to position the test strip correctly. The long end of the test strip points downwards (BOTTOM). The test strip must completely cover the grey fields on the ColorCard. It must not be placed at an angle / carelessly. Otherwise it will also determine the grey background colour and use it to calculate the values. Some people’s problems arose from a false economy - they were halving test strips to save money.
The scanning process is activated after the timer (60 seconds) has counted down and this triggers the auto focus 3 seconds later. Use the 3 seconds to align the mobile phone. If you are too late, you can restart the scan with auto-focus within 7 more seconds by tapping the display. A scan at a later time will give false results because the test strip keeps reacting. Thus, a scan with the same test strip cannot be repeated.
Follow the instructions in the app and remain holding your smart phone while the measurement is taking place.
I hope that the video and this written guidance will help you to carry out your measurement reliably and accurately, and to avoid the typical mistakes made by beginners and professional users alike. You are in possession of a very reliable and convenient tool to help you determine the most important water values in your garden pond, aquarium or tap water.