Managing Pond Water Quality

Keeping fish is not like keeping any other pet, such as a cat, dog, rabbit or guinea pig 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.

1. 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.

2. 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.

3. 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:

1. Loss of appetite

2. Sulking on the pond bottom

3. Hanging motionless at the surface

4. Clamped fins

5. Gasping at the surface.

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

Kill blanketweed and string algae.