Once you have built your pond and filled it with tap-water, the urge to put some fish in it can be enormous. Don’t. A new pond must settle down -six weeks is not an unrealistic time to wait -before introducing fish. During the first couple of weeks the fresh water in the pond will turn a browny-green colour, and become progressively cloudier as micro-organisms multiply. A variety of plants should be in place, including plenty of submerged oxygenators. These will help to absorb dissolved minerals, and of course provide oxygen to the water. The fish will be afforded some protection by these, and will also use them for green food. Floating and deep water plants provide the shade which is very welcome on hot summer days. By the sixth week the water should be clear.
It is worth remembering that most fish scavenge. They’ll nose around and disturb freshly planted aquatics, so it is important to allow the plants time to establish before the fish are introduced, and to cover the soil in the pots with a thick layer of gravel, otherwise the soil will be displaced, and the water will turn brown. Buying some fish from a garden centre, transporting them home, and then putting them in the pond, with no forethought about the environment they were in, and the one to which you are now subjecting them, can result in a high, if not total, mortality rate. So, to start with, it is essential to know just how many fish, and of what size, your pond can accommodate safely. Work this out before you start spending money
Fish make great and comparatively undemanding -pets for children on buying the fish. Of course, you may exceed the recommended quantity of fish under certain conditions if, for instance, you have a pond that is very deep, or you have installed an over-sized filtration system, but this is unlikely for a beginner to the hobby. The best time to stock a new pond, or add further fish to an existing complement, is in late spring or early summer when temperatures are fairly stable but, when buying fish you do take a bit of a gamble. No one can say with 100% conviction whether a fish is absolutely free of disease or parasites, regardless of how healthy it may look.