How to test garden pond water

Time and time again we read and are told that water quality is of paramount importance when keeping fish, especially koi.

It should lie at the centre of every serious koi keeper’s plans, from the moment we start to consider the plan and design of our koi pond, with considerable attention being paid to the shape of the pond (surface area to volume ratio), the size and design of the filter and the materials used in construction.

These and other factors will determine the water quality that our pond will provide for our koi. Cut a corner at this stage and in all probability you are likely to be fighting an uphill struggle to provide koi with the quality they require and deserve.

Koi are like any other fish in that they require specific water conditions in which to survive. This does not mean that koi may simply choose to ‘dislike’ a particular water if it is not suitable. Their physiology negatively reacts to unfavourable conditions, causing biochemical dysfunction and ultimately stress. Consequently, a koi’s body will ‘reject’ such environmental conditions leading to a change in behaviour and an increased susceptibility to disease.

Therefore, maintaining a suitable water quality not only allows koi to thrive, but also prevents them from experiencing stress and the associated health problems. By understanding the processes involved in maintaining a healthy pond environment and focussing our attentions on it, we can enhance the health of our koi without having to pay much regard to the biology of the koi in our pond. In other words, because the water quality is fundamentally the keystone in the ‘bridge’ of koi health, if our water quality is good, the health of our koi will follow.

Water Parameters.

As the world’s best solvent, water will pick up and dissolve the widest array of substances, characterising many aspects of the environment with which it comes into contact. A number of pertinent parameters that are likely to fluctuate and have an impact on koi health are straight forward to measure, identifying the state of the water and to be able to suggest any likely effects that they may have on koi health.

The number of parameters that can be measured is as large as the number of substances that can dissolve in water, amassing to many hundreds of different tests. Yet, as koi keepers we can assume at least that our water supply is safe to drink and meets all legal requirements, which at a single stroke, means that we do not have to test for 99% of the solutes that could potentially be dissolved and harmful to fish health. The remaining few parameters will have a tendency to fluctuate and influence the health of our koi and it is with these that we should be pre-occupied.

By testing the individual parameters, we can soon build up a picture of the current situation in the pond. With a little intuition, we can even use the same data to predict future occurrences and also look back on events that may have occurred historically.

Seven useful parameters that can be tested to generate a comprehensive understanding of the pond environment can be loosely divided into 2 groups: Biological and Chemical.

Biological Parameters.

These include ammonia, nitrite and nitrate and are grouped as biological parameters because they are most significantly affected or controlled by life within the pond.

Ammonia. Ammonia is toxic (which is why koi excrete it), is colourless and is released from the gills, readily dissolving in pond water. It can take two forms, either free ammonia (NH3) of the ammonium ion (NH4+). The ammonium ion is less toxic than ammonia and unfortunately, ammonia will predominantly take the toxic NH3 form in the alkaline conditions of a koi pond. Tests have shown that fish can tolerate higher ammonia levels in more acidic water and as a result may offer a little leeway if an ammonia problem arises in such conditions. However, the only guaranteed way of preventing koi from suffering from ammonia toxicity (whatever the pH) is to keep it at zero.

Nitrite. Nitrite (NO2) is also toxic and is the by-product of the biological (bacterial) breakdown of ammonia. It has a reputation for being more stubborn and persistent than ammonia, with bacteria taking longer to get on top of a nitrite peak.

Nitrite levels can often rise out of control for long periods in a new pond, to levels where even a partial water change (30%) does not appear to reduce the problem. If nitrite levels are allowed to become too excessive, then the nitrite itself can become inhibitory to the nitrite-oxidising bacteria, increasing even further the time taken for levels to drop. These bacteria, which includes Nitrobacter species, break the nitrite down into less toxic nitrate.

Nitrate: Nitrate is the least toxic of the 3 nitrogenous compounds. It can be regarded as the nitrogen bank, where all of the nitrogen from the pond system is deposited. Nitrates will accumulate within a koi pond over time, and can be utilised through plant growth or diluted by a partial water change.

Chemical Parameters.

These include pH, KH, GH and oxygen and are grouped as chemical parameters as their levels are caused by chemical interactions (some of which may be directly related to other biological processes).

pH. pH measures the acidity or alkalinity of pond water. A koi pond’s pH should fall between 7.0 and 9.0, ideally being stable around 8 and 8.5. This slightly alkaline pH (7 being neutral) suits the environmental requirements of koi and with a little effort, should be relatively easy and inexpensive to maintain.

KH. KH is a measure of the soluble carbonate/bicarbonate ions that act as a buffer to maintain a stable pH. A medium to high KH shows that the pH is not likely to fluctuate and is therefore the most desirable.

GH. GH measures the general hardness of pond water, particularly the hardness forming ions of calcium and magnesium. The GH should be medium to high in order to match the conditions that is preferred by the koi physiology.

Oxygen. Oxygen, like all of the preceding parameters is required at a minimum level. It dissolves in water and can be easily added using diffused aeration, venturis, moving water or through plant photosynthesis (although this is less common in a koi pond, unless it is suffering from blanketweed). Water will hold less oxygen in warmer water (just when koi and bacteria require more) and if a pond is excessively planted, may well suffer from dawn depletion as DO levels drop at night through excessive plant respiration.

Why Test? Whenever the quality of a substance is at issue, it must be compared to a ‘standard’ or ‘benchmark’ in order to put it into context. Water quality is no different and when we test a sample, besides analysing it and gathering basic data, we can also compare it against what is desirable. Furthermore, as soon as we are able to measure something, we are in a position to measure it and thus we can manage and ensure that it reaches at least the minimum standard.

If by testing, we can verify that our pond water is satisfactory, then we can gain a degree of confidence that the health of our koi should be satisfactory, at least in the medium term. Furthermore, testing and logging data should allow us to detect any deviations from the norm before it starts to have a significant negative effect on koi health. What better confidence booster could there be than to verify through testing, that your koi are being provided with only the best water quality.

Regular testing will also highlight variations or instability in any of the parameters, allowing you to intervene and improve the quality of the koi’s environment.

How often should I test?

Problems are most likely to occur early on in the life of a pond, including each spring in even a mature pond. A new pond is at most risk from an immature filter being unable to handle the waste that the fish and feeding regime produces, leading to problems at a later date. Even prior to introducing koi, a new pond should be tested for the few chemical parameters to ensure that the source water is acceptable. Don’t fall into the trap of testing a ‘virgin’ pond for ammonia and nitrite prior to stocking as they will both read zero, possibly leading to a false sense of security. These parameters must be tested intensively after stocking and during the first 3-4 months, particularly after any additional fish are added.

Having ridden the potential storm of running in a new pond and avoided the problems of new pond syndrome, the water need only be tested every 2-3 weeks to check when a water change is required, or to confirm that any filter maintenance has not upset the pond’s overall balance. Once you have created a mature filter, guard its health very jealously. With experience, and through becoming familiar with your own pond, it should become possible to gauge the health and condition of your water by watching out for any changes in fish behaviour. If your suspicions are arisen by say a drop in appetite or increase in lethargy, verify your observations with a number of water tests.

What are the ideal results? You must be demanding and precise on behalf of your koi by ensuring that you don’t compromise on water quality. For this reason, the only acceptable levels for both ammonia and nitrite are zero, with nitrate rising no higher than 50ppm. PH should be stable between 7.5 and 8.5 (ideally) with a KH of at least 8odH and a GH of at least 12odH. Dissolved oxygen should never be allowed to drop below 6mg/l.

Testing Procedure:

To ensure that you can compare results effectively, endeavour to take samples at the same time of day. As the concentration of a solute (with perhaps the exception of oxygen) is homogenous through a solution, it should not make much difference from where in the pond you take the sample. However, if testing DO, take the sample from the pond itself rather than a cascade or waterfall.

Both pH and DO can fluctuate naturally throughout a 24 hour cycle (through interactions associated with photosynthesis) so samples should be taken at the same time of the day if direct comparisons need to be made.

How to test (Colourmetric – Tablet or liquid)

Prepare the vial, rinse twice with pond water

Fill the vial with the appropriate volume (mls) of water, using a syringe if necessary.

Add the reagent(s) as described (either tablets or liquid)

Wait the prescribed time for the colour to change.

Compare with the ‘standards’ on the colour chart.

What if there is a problem.

A. A high ammonia or nitrite. This indicates that the rate at which ammonia is being produced by fish and feeding regime is greater than the rate at which bacteria in the filter can break down. Time must be given to allow the bacteria to ‘catch up’ and in the mean time, a partial water change and cessation of feeding should suffice. Only recommence feeding once readings have returned to zero and repeat the process if either levels rise again.

B. High Nitrate. If nitrate exceeds 50ppm, a partial (20-30%) water change should be carried out to dilute it. Testing after the water change should verify that the nitrate level has been reduced to safer levels.

C. Low pH, KH or GH. Add a source of calcium carbonate that can then be used as a buffer to increase pH. This could include limestone chips or cockleshell, placed in a filter.

D. pH, GH or KH too high. This is a sign that excessive minerals, particularly lime (or cement) are being washed into the pond. First, dilute the problem with a partial water change and then locate the source of the problem and seal it.

E. DO too low. This will usually be evident through lethargic fish behaviour or in extreme circumstances, koi gasping. This can often occur very quickly in hot, muggy weather or after a course of pond treatments have been added to the pond. Additional aeration using diffusers or increased water movement should remedy the problem

What if some of my parameters are permanently incorrect?

1. If ammonia or nitrite levels are consistently above zero, go through the following checklist.

a. Is the filter still maturing (ie under 3 or 4 months old)? If so, remain patient while reducing the feeding rate and carrying out regular partial water changes. b. Is the filter mature? If so, have the koi been overfed recently? Has the diet been changed? Do the bio chambers need de-silting? c. Is the filter large enough to handle the stocking level or pond size? You may need to reassess your filtration.

2. If pH is consistently low.

a. Add a source of calcium carbonate to buffer the low pH.

3. If DO is always too low.

a. Use additional aeration on a permanent basis. Consider adding aeration to the bio chambers.

To carry out a water test, you will need:

a. Test Kit

b. Test Vial

c. Measuring Syringe (in some cases)

d. Colour Chart

e. Diary/Data Log.

Kill blanketweed and string algae.