I have built a concrete fish pond. Do I have to treat the concrete before the fish can be introduced? Concrete fish ponds and ornamental pools are simple to construct but require initial treatment to stabilise them before the fish can be introduced.

Treatment can consist of seasoning the pool by filling and emptying it two or three times over a period of a month or six weeks, or by treating it with chemicals.

Seasoning or treatment of the pond is necessary to prevent lime from the concrete killing the fish. If the water is fluoridated it should be conditioned with a water-ager prior to introducing any fish. A few tadpoles or small goldfish should be placed in the pond to ensure that treatment has been successful before more-valuable fish are introduced.

Treatment

The pool may be treated by filling it with water containing alum (a salt comprising a double sulphate of aluminium and potassium) in the proportion of 1 kg of alum to 500 litres of water. After one week it should be emptied and refilled with water containing 1 kg of Epsom salts per 500 litres and again allowed to stand for a week.

Finally, the pool should be emptied and refilled with clean water, then emptied again and refilled after one week. Fluoridated water should then be conditioned prior to stocking with fish.

Once the pool has been stocked and plant life established, it should not be disturbed for at least a year, except for occasional topping-up with fresh water.

Initially, the water may become cloudy, but this cloudiness should disappear again as the plant and fish life in the pond settle down.