Acid Water

When fish are prone to disease, sudden death and red fins, this is a sure sign that the water has a high level of acidity (or low pH). Other indications are when oxygenating plants do not multiply well, biological pond filters do not work properly, and water snails develop thin, pitted shells.

Remedy: see ‘Alkaline water’ below.

Alkaline Water

When fish are prone to fungal diseases and gill disorders, this is a sure sign that the water has a high level of alkalinity (or high pH). Other indications are when oxygenating plants are covered in a slimy coating, water plants display a yellowing of the leaves when in full growth, and the water smells slightly of ammonia.

Remedy: Whether the water is biased towards acidity or alkalinity, the remedial process is the same. To correct the pH level so that it is as near to the desired level of pH7-7.5, start by changing about 25% of the water in the pond. Then increase the aeration level, such as by running a fountain or waterfall, turning on a filter or venturi aeration device.

Green Water

Caused by a vast number of microscopic algae, this is not harmful to fish or plants, but is unsightly and detracts from the beauty of the garden. In new ponds this effect should clear by itself. If not, install a filter with UV clarifier, and then when the water has cleared by half or more, add more oxygenating plants to get nearer to the desirable ‘balance’ of plants to fish,

Smelly Water

A balanced pond with fish, plants, and perhaps a fountain or cascade will have enough ‘going on’ to prevent the build up of gases. If your pond has just a faint odour, then reduce the water level by about half, and use a pond vacuum to suck up the silt and detritus from the bottom of the pond. Then, top up with clean water. If the problem is acute, it is probably caused by a lack of oxygen in the sediment, promoting the growth of certain bacteria, which produce unpleasant gases, such as methane and hydrogen sulphide — which smells of bad eggs. Drain the pond (after first netting out any fish), extract the silt, and refill it with clean water. Installing a filter with UV clarifier should help to prevent this from happening again.

Leaking Concrete Pond

To trace the leak, turn off all pumps and fitters, and allow the water to drop to the level from where it is escaping. The leak may be in the rendering — caused by excessive exposure to sunlight or general wear and tear. Alternatively it may be in the base concrete, due to outside influences such as plant roots growing through it. A small leak can be repaired with an application of rendering. Where the leak is more serious it may be necessary to install a butyl liner as a membrane, which will maintain the water in the pond. Remember, if roots have caused the problem these will need treating before the liner is put in place. If not, they will continue to grow, and will damage the liner, causing the leak to start all over agaipn.

Pond Icing Over

The ice layer prevents oxygen from getting in to the water as well as harmful gases being allowed to escape. If snow then falls, it will settle on the ice and prevent light from penetrating into the water for the fish. Melt a hole with a saucepan full of boiling water, or prevent ice from forming in the first place by using an electric pool heater. Alternatively, run a fountain or waterfall permanently — the moving water never becomes still enough for ice to form.