Managing pond water quality – Regular testing

Keeping fish is not like keeping any other pet, such as a cat, dog, rabbit or guinea pig as they are unable to escape from their pond. If four-legged pets take a disliking to their surroundings or become stressed in their environment in which their owner wishes to keep them, they can retreat for cover until the hazard has passed.

This is not true for fish, which, whether they like it or not, are stuck with the environment we provide for them, whether it is stressful to them or not. How we manage and maintain the water in a pond will have a direct effect on the health and growth of our pond fish. For example, fish are constantly excreting toxic waste into their own living space and they will eat, breathe, and even drink that same water. We must ensure that we can optimise the water quality experienced by our pond fish, otherwise we should expect a string of health and disease problems.

How can I optimise the water quality in my pond?

Fish in natural lakes, ponds, rivers and oceans fair very well where stocking rates are typically a lot lower than in a garden pond and where a balanced, thriving ecosystem is maintaining a healthy water quality. Problems can occur in a small pond where the number of fish can be unnaturally high. This is accepted as the norm, and should not lead to a decline in water quality if a number of guidelines are followed.

A pond filter is an essential requirement. Fed by a pump, it’s job is to remove solid waste from the pond, keeping the water clear and to breakdown the soluble and invisible toxic fish waste in less toxic by-products. This is achieved over time by beneficial bacteria that naturally colonise the filter media.

Feed fish sparingly, bearing in mind that the amount of food eaten by fish is directly related to the amount of toxic waste they excrete. If too much food and too many fish are added to a pond then water quality and fish health problems are likely to arise.

Carry out regular partial water changes. About 10-20% of water should be changed every 3-4 weeks in spring and summer to dilute the build up of stubborn toxic by-products. A water change will also ‘freshen-up’ a pond, having a noticeable and positive affect on fish behaviour.

Endeavour to treat raw tap water with a conditioner when carrying out a water change as tap water may be good enough to drink, but is not guaranteed to be fish friendly.

4. Add aeration. This is easily achieved by placing the return of the filter down a waterfall or attaching a fountain to a pump. The extra agitation of the water will increase to dissolved oxygen content, which can drop worryingly low in the warmer summer periods.

What affect does water quality have on fish?

Water quality has a very direct and predictable influence on fish health.

Poor water quality = Poor health

Good water quality = Good health

As fish are unable to escape poor water quality, they must suffer the stress of swimming in a soup of toxic compounds which they have excreted – not a healthy situation. This makes fish more susceptible to disease, and a downturn in water quality is usually causes a change in fish behaviour.

Watch out for:

Loss of appetite

Sulking on the pond bottom

Hanging motionless at the surface

Clamped fins

Gasping at the surface.

All these changes in behaviour will usually indicate a deterioration in water quality.

What is good water quality?

Good water quality is a measure of how suitable water is for keeping fish healthy. There are a number of simple tests that can be carried out on pond water to determine whether it is suitable. The first thing to do upon noticing a change in your fish’s behaviour is to carry out a water test, to determine the cause of the problem, which will allow you to resolve the problem, preventing it from happening again.

What do I test my water for, and what am I looking for?

There are well over a dozen different test kits available, each testing for a specific water parameter. Do not let this put you off, as there are only really 2 or 3 that you should need to use to give you useful information rapidly.

1). pH. This is a measure of how acid or alkaline the pond water is. Pond water must be above 7 and no higher than 8.5, or 9 at a push.

If upon testing your water is within this range, then leave well alone. Tap water is made alkaline by water companies, so regular water changes should help to keep your pH acceptable.

If your pH is below 7 (acidic), then a water change or the introduction of lime stone chippings in the filter will bring it back up to the desirable range. If your pH is above 9, and too alkaline, the probable cause is the running in of untreated lime into the pond. Seal any surrounding cement work with a clear plastic sealant.

2). Ammonia. This tests whether the toxic waste (ammonia) that fish excrete is being broken down. An ammonia test is only usually required when a new pond and filter are being matured over the first couple of months and there is a question over the functioning of the beneficial bacteria in the filter. 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.

3). Nitrite

Nitrite is a persistent toxic by-product of the bacterial breakdown of ammonia. Although it is slightly less toxic than ammonia, the bacteria involved in breaking it down further are slower to act than those involved in the breakdown of ammonia.

The 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. Similarly, the water need only be tested for nitrite in the early weeks of a pond and filter, while the bacteria responsible for its breakdown become established. Once the filter bacteria have colonised to the level of your stocking and feeding rate, a nitrite reading should not occur again as long as the feeding and stocking rates remain pretty constant

How do I test?

Test kits typically use a change in colour to measure a water parameter. A sample of water is taken from the pond, filling a clear test phial. Either a series of liquid re-agents or a tablet are added (depending on the manufacturer), and the sample is left for a set time, waiting for the colour to develop. The final colour is simply compared to a chart to determine the reading. It’s as simple as that.

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 the experienced eye to assess the quality of your water by simply assessing the behaviour of the fish. 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.