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Photometer vs Liquid Test Kit vs Dip Strip Test Kit?

by Chris Thomas January 16, 2024 9 min read

Photometer vs Liquid Test Kit vs Dip Strip Test Kit? - Kitsu Koi

Testing your pond water is an important part of the hobby. Water quality plays a part in the overall health of the pond and your koi. It is also a contributing factor to the growth of koi, and the appearance of your fish. 

Hobbyists will at some point have to decide what parameters to test for, and what equipment is suitable for their needs. Every koi keeper should have access to something to test the basic water parameters - Ammonia, Nitrite, pH, KH (carbonate hardness), and Total Chlorine. Those five test parameters are the ones most likely to cause problems for most fish species. 

In some kits, you will find Nitrate and Phosphate tests, but they are not as important as the others. Their effect on koi health is far less significant than pH, Ammonia, and Nitrite. Nitrate and Phosphate levels can be easily controlled by sensible stocking and regular water changes. An abundance of Nitrate and Phosphate can cause increased algae growth - quite a visible indicator that Nitrate and Phosphate are in need of control. 

When testing our pond water, we require accuracy and precision. Accuracy and precision are two measures of observational error. Accuracy is how close measurements are to their true value, while precision is how close the measurements are to each other. A good test kit will provide both accuracy and precision. 

When assessing the precision and accuracy of a test kit, you must take some accountability for your consistency when preparing samples.. If you are using sensitive equipment (a 'sensitive' test kit would be something described as low range, where the unit is measuring a narrow range of very small numbers. An example would be the Hanna Ultra Low Range Total Chlorine Pocket Checker - designed for reading Total Chlorine from 0-500 parts per billion). When using sensitive test equipment, the results can vary significantly by changing your method. Taking longer to mix the reagent for example, or starting your timer at different stages of the process can interfere with your test results. 


Using a syringe to collect a sample of pond water

When taking a sample of water, it's wise to use a syringe to collect an accurate amount of water. Using a syringe reduces errors from different sample sizes


Accuracy and precision, naturally, can come at a cost. We would advise spending as much as needed to get the job done. For example, if you live in an area known for hard water, you wouldn't need a particularly special test kit for pH and KH. However, in water with a higher pH, measuring Ammonia would be of the highest importance due to the toxicity of Ammonia. It would be the opposite for the koi keeper living in a soft water area such as Manchester or South Wales. If you have soft water, maintain a stable pH would be a priority, and if your pH is 7.5 or less, than the majority of ammonia would be present at Ammonium, which is non toxic. 


Photometers, liquid drop test kits, and dip strips use a very similar method to complete the same task. A reagent is mixed with water, and a colour change is observed. 

Hanna Pocket Checker cuvettes, one plain sample, and one with reagent

The sample on the left is used to 'zero' the photometer. The sample on the right represents a sample of pond water with the reagent added. The reagent reacts with the target chemicals to change the sample colour. The photometer then measures how much light the sample absorbs, and calculates the result. 


In the case of a photometer, usually two samples of pond water are taken. One is used to 'zero' the photometer. A calibrated beam of light is passed through the sample and measured. This allows for any tint in the water to be removed from the later calculation. To the second sample, a reagent is added, and after a specified reaction time, the colour change is measured, again, by passing a beam of light through the sample and measuring how much light passes through. The photometer will correct the result for the colour in your pond water automatically from the first sample recorded. The photometer will display a digital read out of the result. 

Photometers are very accurate and precise. The photometers popular with koi hobbyists are laboratory derived devices and as such have a data sheet with specifications. In the specifications, it will detail the range, resolution, and accuracy.


Hanna HI-761 ULR Pocket Checker Specification


  • The range is the upper and lower limit capable of measurement by the photometer and intended reagent
  • The resolution is the smallest interval the photometer can display
  • The accuracy is how close the measurement will be to the true value
  Hanna HI-761 Total Chlorine, Ultra Low Range
Range 0 - 500ppb
Resolution 1ppb
Accuracy ±5ppb ± 5% of reading
Method Adaptation of the USEPA method 330.5. The reaction between the chlorine and DPD reagent causes a pink tint in the sample.


The table above shows the main specification for the Hanna HI-761 Total Chlorine, Ultra Low Range Pocket Checker. Looking at the specifications will tell you whether this is the right model for you. If you are unsure, then call, and we can advise the correct unit. 

Using the table above as an example, let's explain the range, resolution, and accuracy. The range of the Hanna HI-761 Total Chlorine, ULR is 0 - 500ppb, so the maximum reading it can measure is 500ppb, or 0.5mg/l. The resolution is listed as 1ppb, which means the results will be displayed to the nearest 1ppb. This unit can display readings as low as 1ppb, which is 0.001mg/l. The accuracy is listed as +/-5ppb +/-5%. That means the result will be within 5ppb of the true level, +/- 5% of the reading. 

Hanna Instruments manufacture other Total Chlorine testers with different ranges. The HI-711 Total Chlorine has a range of 0 - 3.5ppm. This range is 7x larger than the HI-761, as 500ppb = 0.5ppm (parts per million). In a koi pond, the maximum Total Chlorine allowable is 0.02mg/l or 20ppb. Because of the testing range and resolution offered by the HI-711 and HI-761, we would choose the HI-761 as the intended range and resolutions suits our needs better.

1ppt (parts per thousand) 100mg/l
1ppm (parts per million) 0.1mg/l
1ppb (parts per billion) 0.001mg/l


Compared to liquid test kits and strip test kits, photometers offer better ranges and resolutions for taking a closer look at the true value of our pond parameters. It is almost impossible for our eyes to differentiate between the colour changes that a photometer is capable of detecting. If you require results in very small ranges, then the photometer offers the most capability. 

The serious koi keeper, or for anyone that just loves gadgets, the Hanna HI-83303K is a complete bench top photometer that measures multiple parameters. The main benefit to a bench top photometer is the ability to log your results. 


Hanna 83303K bench top photometer for koi keepers

Our Hanna 83303K Benchtop Photometer in action. Our water supply is low pH and KH, so the precision, accuracy, and resolution is required. The 83303K also logs our results, which helps us keep track of any trends in the water quality. 


Photometers are the most expensive type of test kit available to koi keepers, but they provide the best information to the koi keeper. 

If you wanted a set of photometers for testing the water in your koi pond, then I would recommend the following 

  • HI-700 - Ammonia, Low Range
  • HI-707 - Nitrite, Low Range
  • HI-761 - Total Chlorine, Low Range
  • HI-775 - Alkalinity (KH, carbonate hardness) 

We have made this bundle available to purchase from our online store at a discounted price. 

Liquid Test Kits

The liquid test kit is perhaps the most used type of test kit used by koi keepers. Most liquid test kits use one sample of pond water, without any correction for colour or turbidity of the pond water. Following the instructions provided, one or more reagents are added to the sample, and after the required time, the colour of the sample is compared to a colour chart (with the exception of KH (carbonate hardness) usually, in which the drops added are counted until the sample changes colour). This relies on the user correctly interpreting the sample and charts.

A common error I see online is people sharing pictures of their test, and displaying the sample and colour chart incorrectly. The test cards must be read as described in the instructions. If you don't view the test card correctly, then you will get results with poor accuracy. 

The resolution of liquid test kits is much higher than the resolution of a photometer. It's not possible to print so many colours on one chart, and expect a user to be able to differentiate between the small differences. For example, most liquid test kits for Ammonia will read 0.25mg/l as the first interval, compared to the Hanna HI-700 Ammonia Low Range Pocket Checker, which can read as low as 0.01mg/l. 


Colombo pH test Result Card

Liquid test kits do not have the same resolution as a photometer, though in some cases can provide enough information for the hobbyist. Using the colour charts correctly is important for accurate results. Here you can see the test vial sits in a circular cut out. You should remove the cap, and view from directly above.


Liquid test kits are available from a few manufactures serving the koi hobby, but our most popular is the Colombo Test Lab Professional, which contains the reagents and colour charts to test Ammonia, Nitrite, Nitrate, pH, KH, GH, and Phosphate. It is also possible to buy the individual tests. We use the Colombo as a back up for our photometers - in cases of battery failure, or as a check for unexpected results. 

 Colombo Test Lab Professional - Contents


Dip/Strip Test Kits

Dip/Strip test kits work slightly different to the photometer and liquid tests, where reagent is added to the water. The reagent is contained in an absorbent pad on a strip of plastic. The strip is dipped in to the sample of water, and the water reacts with the reagent the absorbent pad. The strip is then held up against the colour chart, usually printed on the packaging.

These tests are the least reliable in the opinion of experience koi keepers, koi dealers, and koi educators. They can be hard to read, suffer from inaccurate results, and are easily spoiled. 

However, they are cheap, usually a quarter of the cost of a liquid test kit. If it's a case of using a dip type test, or none, your fish will be better off using a dip type test. 

If your choice is to use a dip/strip type test kit, if you get any results you think require further examination, then a local koi club, friendly koi keeper, or your local dealer could provide better water testing for you.

Obviously, if your water supply is on the soft side and you require accurate pH and KH results with a low resolution, then I wouldn't recommend them. The same goes for people who are heavily stocked and need to carefully monitor ammonia and nitrite. 


Dip type test kit, sample contamination

A common problem with a dip type test strip is contaminated samples. The water and reagent from one pad and run in to the other pad, staining the sample and changing the colour of the sample.


Understanding the Results

If you have a liquid test kit or a dip/strip test kit, then you have an estimated result of any parameter. Due to the resolution of the liquid type test kits, you should be aiming for the following 

  • Ammonia - Your Ammonia result should be 0mg/l on any liquid test kit or dip/strip type test kit
  • Nitrite - As per Ammonia 
  • pH - Koi will tolerate a pH between 6.5pH and 9pH. With liquid/strip test kits, I would want this reading to be between 7.5pH and 8.5pH to leave room for any errors in reading the colour charts
  • KH - KH is subjective, but 4-8dKH is where most koi keepers would be happy (and the fish). If your KH is consistently lower than 2-3dKH, then I would invest in better test equipment
  • Chlorine - The common method is to use DPD tablets if you don't have a photometer. You should have ZERO colour change to indicate no chlorine present

If you have a photometer, then most will need some kind of conversion to give you a result most koi keepers will be able to understand. Most test kits, including photometers are 'dumb'. They do not understand what Ammonia or Nitrite is, and detect more simple chemicals or elements, and apply a conversion. Some units will display the converted amount, some will include instructions. The Hanna Pocket Checkers for Ammonia and Nitrite include the conversion factor in the manual but I will provide a table for those below. You don't actually need to convert the reading every time, if you convert the maximum allowable value to the units used by your chosen photometer. 

When using the Hanna HI-707 Nitrite Low Range, you need to multiply the result by 3.29. The maximum nitrite reading in a koi pond should be no more than 0.2mg/l. If we divide 0.2 by 3.29, we get 0.06mg/l. As long as your result is lower than 0.06mg/l on the Pocket Checker display, there is no need to perform a conversion each time. 

Other Testing Tools

From time to time you may want or need to test other parameters, or may want constant monitoring of your water quality. 

If you have a specific need to test for metals, then photometers are again the best option, with Hanna offering a Pocket Checker for most metals that can be present in your water supply, and affect your fish. We recommend constant monitoring of pH for anyone using RO, or with particularly soft water supplies, to avoid a pH crash. Some constant monitors such as Seneye do more than pH - it can monitor ammonia and temperature, and uses the cloud to give you the information anywhere in the world. 

The most common, electronic water tester is the salt meter. The popular model is the Koi Medic Salinity Meter. I've owned one of these for over 20 years and it's essential for the proper dosing of salt in a koi pond. An accurate salt meter has other uses too, such as calculating the volume of a pond. How, you ask? Check out our 5 Ways to Measure your Pond Volume post.



Chris Thomas
Chris Thomas

Chris has been keeping koi for over 25 years, and dealing in koi for 15 years. Travelling to Japan to select new stocks is the favourite aspect of the business, closely followed by being on the tools pond building.

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