FAQ: Pond Fish Problems

There’s something very special, not to mention relaxing, about idling away a moment or two on a hot summer’s day watching fish languidly swimming their way through the water of a well set-up pond.

Unfortunately, no matter how apparently natural-looking the scene appears, it is, of course, an entirely artificial one and that means that however carefully you stock your fish-pond, it’s likely to be home to more fish for its size than a truly natural one.

As a result, keeping fish can bring its share of problems, but fortunately many of the common ones can be overcome, principally with a bit of care and vigilance and having the answers to some of the most frequently asked questions should help you avoid many familiar snags.

So, how do I avoid overstocking?

The pond’s surface area is the biggest single factor in deciding stocking levels, so you need to work this out first. It’s not a difficult calculation – all you need is the average length and width of your pond, and it doesn’t matter if you’re happiest working in metres or feet and inches! The golden rule is allow 25cm of fish for every square metre, or 1 inch of fish per square foot and you won’t go far wrong.

In practice, it’s always a good idea to allow a little under the maximum you can get away with; remember, you’re probably wanting your fish to grow!

Yes, but how do I know they won’t outgrow my pond?

Picking the right sort of fish is an important part of making sure you avoid problems, so you sometimes need to balance what you’d like with what you can realistically hope to accommodate. It’s easy enough to avoid the obvious potential giants that everybody knows about, such as koi, but others, such as the European catfish – often sold as a “pond cleaner” – which can grow to 5ft (1.5m) or more aren’t always so familiar. Even the commonly sold orfe can grow to a foot (30cm) in length, so it’s essential to do your research first, especially if you don’t have a particularly large pond.

How can I avoid disease?

The best way to avoid disease is to ensure that any fish you put into your pond are fit and healthy to begin with; many fish illnesses spread quickly in the confines of a pond, so it’s just not worth the risk. Pick fish that have bright eyes, don’t have missing scales or any signs of damage, have strong upright fins and seem to swim freely and easily and you shouldn’t go far wrong.

What are the particular signs of disease to look out for?

Avoid any fish which have:

  • Cotton-woolly patches on their bodies
  • Bloated bodies or “life-less” eyes
  • Raggedy, torn fins
  • Patches of lost colour or pattern
  • Holes, ulcers or rubbed patches of skin
  • Visible parasites

The person at the garden centre said I should test my water quality. Why?

It is often said that nine-tenths of the problems with fish come down to poor husbandry, and that water quality is probably the single biggest contributory factor. Fish live their lives surrounded by the water you have in your pond – an obvious point, but a vitally important one. The very fact of their existence means that the chemistry of the water is constantly changing; some five per cent of their food each day gets turned into ammonia, for example, and then excreted into the pond. Quite apart from what they do themselves, a whole range of elements including garden chemicals, the material of the pond and the hardness of the water have a very direct effect on their world, and the only way you’re ever going to know that anything is starting to go wrong – at least before it becomes too late – is by testing.

I think a heron / a fox / next door’s cat is eating my fish. What can I do?

Unfortunately, this is an age-old problem. Provide what is effectively a fast-food outlet for predators and the outcome is inevitable – the expression “shooting fish in a barrel” has never been more true! Although these three do use different approaches to their hunting, the end result is the same but so, fortunately for the pond keeper, is the solution; it all comes down to deterrence and denial.

A stout mesh is the usual choice to help keep your fish from becoming an easy meal and it doesn’t have to be an ugly, intrusive eye-sore; many modern designs are quite attractive in their own right, while some can be suspended at or just below the surface. Alternatively, a number of companies offer a range of PIR-triggered devices, ranging from fake “gunshots” to squirting hoses that can be helpful to make things awkward and unpleasant for visiting predators.

If you live in an area where herons, foxes or neighbourhood moggies are likely to be a problem, you are almost certainly in for a constant battle and you’ll need to be ever-vigilant. The trick is to stop your fish from being an easy target, but act quickly as soon as you spot trouble; once these creatures find a ready food supply, they’ll keep coming back.

Fish and garden ponds are, unsurprisingly, natural partners; with a few precautions and a healthy spot of vigilance, you can make sure that they always complement each other perfectly.

Last Modified: January 25, 2022