Testing Pond Water Quality

As pond keepers, we spend a great deal of our pond budget on buying a pump and filter so that we can provide our fish with a good healthy environment. Water quality has a very direct and predictable influence on the health and well being of our fish.

Poor water quality = Poor fish health

Good water quality = Good fish health

But how can we objectively measure how effective our pond filter is, or how healthy our pond water is other than by looking at the fish themselves? Sometimes relying on observing fish behaviour may not pick up subtle changes in water quality and may also only highlight a problem when it’s too late. The most accurate way of keeping on top of your pond is to test it regularly.

Do I need to test my pond?

Put simply – yes! If you don’t measure it – how can you manage it? By testing regularly, understanding what the results mean, and by responding correctly, you are able to provide your fish with the best water quality. Looking at it another way, it is also better to confirm that all is well in your pond with regular testing rather than only testing your pond once you have problems in an attempt to determine the likely cause.

What do I need to test for?

Water is a marvellous substance. It is essential for life and performs many different dynamic functions. It can adopt an unlimited number of characteristics, being shaped by its environment and in turn, affecting that same environment through its changing composition. Because of its seemingly endless capabilities as a solvent, we could in reality test water for each of the myriad of compounds that can dissolve into it. This would make water testing impractical when trying to gauge a water’s suitability for fish.

Consequently, we tend to rely a great deal on the assumption that our water source is empirically suitable and non-toxic to fish so that we can limit our investigations to only a handful of tests. For example, we do not test our water for mercury, arsenic, cyanide etc as we do take our water to be safe. We do however, test for the more likely and influential factors that can affect the pond environment on a regular basis. We could test our water each day for say, its gold content, but it would be unnecessary to do so as we know that gold levels are not likely to change and that gold does not influence our fishes’ health as much as other key characteristics. So what are the parameters that we should be testing?

There a over a dozen different pond test kits available, each testing for a specific water parameter. This could be daunting as it suggests that testing water is likely to be expensive, lengthy and requires a degree of chemistry. Do not be alarmed as there are essentially 3 key test kits that you should consider as these give you a useful snap shot of the health and risks in your pond or aquarium. Should you wish to delve deeper into the chemistry of your pond or aquarium, then you can also test for more diverse, but less critical parameters.

a. pH. This measures the acidity or alkalinity of your water and acts as a quick and useful guide to its suitability for fish. If the pH is unsuitable, it will stress your fish and lead to health problems. In order to make a judgement as to the suitability of your water, we need to know the pH requirements of your fish. Pond fish prefer a stable pH between 7.0 and 8.5. From a fish health perspective, it is far more desirable that the pH is stable within these limits, rather than erratic.

b. Ammonia. Where the pH of water is tested prior to introducing fish (as well a checking that it is maintaining a satisfactory level) water is tested for ammonia during the maturation of a filter or while fish are being stocked. Ammonia is the toxic substance excreted by fish which must be broken down by bacteria in a filter. If it is not broken down faster than it is released, it will accumulate and cause the fish stress. Ammonia test kits are used to check that the filter is coping with the waste produced by fish.

c. Nitrite. The bacteria responsible for breaking down ammonia act quite quickly, converting it into nitrite which is still toxic and more persistent in an aquarium or pond. A different range of bacteria break nitrite down into relatively harmless nitrates, but can take a long time to do so. Consequently, nitrite tests should be used to ensure that the filter is mature enough to cope with the current stocking and feeding regime.

Other tests include:

d. Nitrate is regarded as the ‘nitrogen bank’ where all nitrogen from ammonia and nitrite is eventually deposited. It is only harmful in excessive concentrations (>50ppm) and can be removed through plant growth (either a vegetable filter or blanketweed!) or through fortnightly/monthly partial water changes.

e. KH. This is a measure of the pond’s ability to resist swings in pH. The higher the KH, the greater the pond’s buffering capacity and the more stable the pH. The KH can be maintained at a satisfactory level by adding calcium carbonate compounds to the filter.

f. GH. A measure of the general hardness, which also has a loose relationship with pH and KH. As ornamental pond fish are hard water fish, a high GH should be maintained through similar methods used for pH and KH.

How frequently will I need to test my water?

Water should be tested regularly for pH to ensure that it is maintained at the correct level. Water used in water changes should also be tested to determine that the pH is desirable. Ammonia and nitrite are tested very frequently during the running in of a new pond. These tests will show how the filter is maturing and whether it is keeping pace with the rate at which waste is being produced. Once your pond or aquarium is fully stocked and has been running satisfactorily for several months, there should be little need to use ammonia or nitrite test kits.

In more mature ponds, test kits can be used to confirm that the hardness and nitrate levels are satisfactory, having a tendency to become a concern as ponds start to age.

The last time I used test kits I was in a chemistry lesson at school. I’m certainly not a chemist, so how easy are they to use?

All test kits or testing equipment are made with the fishkeeper in mind and are easy to use and interpret.

A. Colourmetric Test Kits. These rely on a chemical reaction between the water and a reagent which results in a colour change that can be compared against a colour chart.

i. Liquid. Drops of liquid reagent are added to a measured test sample of water and allowed to change.

ii. Tablet. Instead of drops of liquid, dry tablets are crushed and dissolved in the sample water and the colour change compared to a chart.

iii. Test Strips. Plastic strips, impregnated with reagent are dipped into the sample water and allowed to react, causing a colour change.

B. Electronic Tests. A range of pocket sized digital meters are available, giving a numerical reading. Digital meters are accurate and require regular calibration against known samples but are considerably more expensive than colourmetric tests.

Once I’ve tested my pond water – what next? How do I know what is desirable and what is not?

The time and money spent on testing water would be wasted if the results were not acted upon. If having tested your water, you discover that the water quality is not as good as it could be, appropriate remedial action should be carried out immediately.

  • pH. If pH is too high: Carry out a partial water change with soft, acidic water and check for sources of buffer in your pond or aquarium that could be raising the pH.

If pH is too low: Add some treated tap water (which is artificially buffered) or add a source of lime such as limestone chippings or crushed shell.

  • Ammonia. This tests whether the toxic waste (ammonia) that fish excrete is being broken down. The desirable ammonia reading is zero, but should a positive reading occur then carry out the following:

1.  Stop feeding

2.  Do not introduce any new fish

3.  Carry out a 20-30% water change

4.  Only start feeding when reading is back to zero (this may take a few days). Carry out a test each day for the next week.

However, if a positive ammonia reading reappears upon daily testing, carry out steps 1-4 again. As the filter matures, an ammonia reading is less likely to occur.

  • Nitrite: The only desirable nitrite reading is zero, and if a nitrite reading is present, it is an indication that the filter is not coping with the amount of waste being produced.  Even a low nitrite reading is undesirable and if present, the same procedure (1-4) for ammonia toxicity applies.

Nothing substitutes for experience

Once you have kept fish healthily for a season or two, and managed the water quality in a pond successfully, the need to test your pond water regularly should reduce.  It should become possible for your experienced eye to assess the quality of your water by simply assessing the behaviour of the fish.

These changes in behaviour will usually indicate a deterioration in water quality.

Watch out for:

1. Loss of appetite

2. Sulking on the pond bottom

3. Hanging motionless at the surface

4. Clamped fins

5. Gasping at the surface.

You’ll be surprised as to how accurate your observations can be and how your experienced eye can become as accurate as the best test kit.  It can certainly work out quicker and cheaper!

Kill blanketweed and string algae.