Choice of water Testing

We are all like that. We want the best that our money can buy. Sometimes we simply want the best car to drive out from behind our walled properties into the street. But when we sit back and consider the options, our senses override our pride. The money in our pockets speaks.

So it is also with testing the parameters of water. We would all prefer meters with probes instead of any of the mundane tablets, strips or dripper bottles. We prefer digital readouts from colour charts and comparators. But is a quick-dip digital pH meter that records to two decimal places not better to have than a pH strip? Or is it just more ‘cool’?

I am not going to bore you with a discussion into analytical instrumentation, but let’s look briefly at the options when you venture out to get a measure of a water quality parameter of your choice.

  1. A simple colorimetric chemical test kit that creates a colour change on a test strip, or by adding drops or tablets of reagent to a test sample. A colour chart or comparator gives you an indication of the concentration of the parameter in question.
  2. A more advanced colorimetric chemical test kit. The colour change is determined by measuring the transmittance or absorption from a specific light source and converted to concentration.
  3. A meter that measures the conductivity of an applied potential to the sample that can be configured and calibrated to give an indication of salinity, TDS (total dissolved solids) and monitoring a host of industrial processes.
  4. A meter that accurately measures the current created of an electrochemical cell against a stable reference.  The probe is made to react to a specific ion like hydrogen ion concentration in the typical pH meter. They use a membrane the separate the tested sample from the inner probe. Can be made to be very accurate and measure a host of different parameters with ion or reaction specific probes. Inter alia pH, oxygen concentration, ammonia, chloride, etc.
  5. Beyond this we have a host of complex analytical instruments for quantifying and qualify almost anything we think of. That is for a labatory.

The decision should be:

  1. Do I need that extra digit in accuracy? Will it make me a better manager or pond keeper, can I stick to the program or will keeping it accurate be too much hassle so that I stop taking the measurement.
  2. What will the meter or test kit cost.
  3. What will reagents and calibration fluids cost in the long run. (Like printers you may end up spending more keeping it running than the actual device.)
  4. What is the skills level required to get the correct results, consistently.  Can I leave the testing in the hands of staff and then base my water management on the results in a log.

SO below is a number of do’s and don’t to think about when you have a decision to make:

  1. Choose an appropriate method of measuring for what you need.
  2. If you don’t need a resolution that will give you two or three decimal places,
  3. Record your reading, not only date but also time
  4. Always record the temperature
  5. Always follow the same correct regime for collecting and processing the sample.
  6. Do not keep samples, measure as soon as possible
  7. Take measurements in the morning before feeding. These readings should be as far as possible from the last feeding. It represents the residual concentrations of what the fish are subjected to and indication of their stress condition.
  8. Always use clean sampling tools and flush two or three times with the sample to be taken. This should apply to both the sampling vessel and the testing container.
  9. Always do final rinse with clean/distilled/de-ionized water (whatever is called for) and let dry upside down in a dry rack for future use.
  10. Don’t let coloured fluid stand in a measuring vial longer that is should. Over time it stains the plastic or glass and might render it useless.
  11. Don’t handle vials for colorimetric determinations by transmittance/absorption by the bare hand. Use a clean tissue.
  12. Deposits inside the vial due to high hardness levels may also lead to undetermined results. 
  13. Be aware of the possible contaminants. Medications and other additives can affect the outcome. A slow change in pH, calcium carbonate, nitrate etc can lead to erroneous and finally indeterminate results.
  14. Meters, test kits irrespective of their type, will always need reagents, calibration fluid or a change in membranes or probes during their life time. Take that into consideration when you calculate the overhead costs.
  15. A meter that is not maintained is useless. All electronic meter “drift” over time and need readjustment.
  16. Change membranes and probes as prescribed
  17. Calibrate measuring equipment as often as prescribed.
  18. A meter that is not calibrated is a waste of time.
  19. Always shake a reagent bottle once or twice before use. Close immediately after use.
  20. Make sure that you use the same reagent cap to close it with.
  21. Do not spill or spatter reagents. It may be caustic and will burn hols in your clothes or burn you. Immediate clean with ample water or as is advised.
  22. Carefully remove the crust that tends to form around some reagent bottles. Do it over a sink with a tissue and flush it away.
  23. All colorimetric reactions are time and temperature dependent and will take time to develop optimally. Wait the prescribed time for the reaction.
  24. All reagents have an expiry date.
  25. And lastly. If you are going to use colour as the determinant, make sure you or your staff are not colourblind.

Different needs require a differed approach. Depending on the complexity of managing your facility, you will need regular or continuous monitoring of the parameters. You will have a preset method of sampling and calibrating your equipment. It is your job and you cannot be sloppy. In a production environment you are working at an optimum and systems running at a knife edge. You need those results and you need them accurate for your assessment. You need correct equipment for the job and qualified people to perform the tests.

As a regular pond keeper you can relax and not worry at all about the consequences. Fish will merely grow slower and might live in a stressful environment. You don’t know and don’t really care.

But as a concerned keeper of fish you want your pond at optimum. Make sure your biological filter is working. But it is not necessary to know that the ponds ammonia is 0.15 or 0.10 mg/l? At the same time relying on a test strip that test for pH, nitrite, nitrate and hardness and NOT for ammonia concentration is foolhardy. It is a vital parameter. You have to understand what you are testing and why. Getting a colorimetric test kit is probably sufficient. A digital one is your choice.

Servaas de Kock

Colorimetric analysis is a method of determining the concentration of a chemical compound in a solution with the aid of a color change in a reagent.