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FAQ: Pond Fish Problems

By: Dr Gareth Evans - Updated: 18 Jul 2020 | comments*Discuss
Fish Ponds Natural Water Quality Health

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.

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Unfortunately whilst putting plants onto shelves in our newly established wildlife pond aquatic compost was washed into the water. The pond is quite murky now, will this eventually settle? If not how can I try to clean the water? Thanks
Paggle - 18-Jul-20 @ 1:29 PM
Good afternoon, I have a small pond and recently I used pond clear to make my pond clearer. As I live in a flat I can't have a electric fountain so I have a solar one with a small filter. I noticed a week later one of my goldfish skin looks like it's been melted ?? the other fish seem okay. So I am wondering did this particular fish have a bad reaction to the pond clear...I know it does say on the bottle harmless to fish. Since this has happened I have emptied the pond with fresh water...he seems to be swimming and eating okay...just hope he will be okay. Would be grateful for any advice. Thank you Tanya ????????
Tan - 8-Jul-20 @ 2:07 PM
Hi there,I have had a ghost koi and he got rather big developed a big fat belly,he had this condition for a good while.then developed skin fungus on him so took him put in different tank and treated him medication and treated main pond ,fish has died.my question in should I clean out pond and is there a way of disinfecting pond and what to use or should just use clean water. Cheers steve
Steve - 21-Apr-20 @ 8:58 AM
Hi I have a smaller type pond approve 12x6ft and almost 5ft deep .I did a water change in March using.the chemical to decloranate tap water .have taken top 5/8ins off.about 2 weekly to freshen water . I have a evergreen for at the end off the pond slightly over hangs the pond....about 4 days ago .I lost 2 koi and today 2 more .I have had them since they were tiny 2" long approx 3 yrs.and today they are a dead in the pond there were about 6 koi originally and about eight small orfe approx now 4/5"long .I feel broken hearted. there is a Lily for cover and some marginal plants.these are not in pond in a dip built into man made pond .any ideas .fish are fed nightly .Lily plant look healthy.repotted this spring into new pot with pond compost from aquatic shop all going very well in until this week. Any understanding to what's gone wrong .I really have no idea the garden secluded .An oldmerrella, cherry tree nearby .And small lavinda bushes. flowers ECT. also near by. Await your help .just going to fish out all their bodies ..
Gina - 22-Jun-18 @ 2:53 PM
Hi i have had 3 fish chased by the rest in the pond , 2 of them have since died and the 3rd looks very still and quiet. Why would this be happening ?
rik - 26-Jul-17 @ 9:41 AM
Hi - I'm wondering if there are any cold water fish that would be suitable for a very small above ground pond/water feature? It will hold approximately 90 liters of water - which I understand is far too small for goldfish/shubunkins etc - but are there any other fish (only one or two of them even) who would be happy in this space? Many thanks in advance for any advice.
Nell - 16-May-17 @ 8:41 PM
Hi there, I hope you may be able to help me as we are getting more and more concerned. For the past few weeks now one of our goldfish in the pond has been laying at the bottom on its side. It seems to be breathing through the mouth but shows little desire to move. When it does move it only swims a short distance before stopping once again. There are approximately forty other goldfish and none of them appear to be affected. Our retailer believes it is suffering from swim bladder and upon advice we have replaced the UV lamp and chemically treated the water. They also suggested offering peas to assist potential constipation but the fish has showed no interest. I fear for the worst and were advised that separating the fish to for treatment could prove fatal. Can you please advise if there is anything we an do? Thank you for your time.
n/a - 17-Apr-17 @ 4:43 PM
I have a golden ore which has been lying on the floor of the pond for the last month as soon as I touch him he darts round the pool then a few minutes later back on the bottom he is about 18yrs old and 18ins long is it time to say goodbye Ken
Smiler - 11-Mar-17 @ 12:45 PM
Cleaned pond few days ago water is clean top 6inches but yellow below.now fish are swimming around the top and the smaller fish are gasping on surface. Help shanks
Sam - 30-Aug-15 @ 7:28 PM
I am trying to find something I can put in my pond to separate larger fish from the fry I am about to get maybe some sort of netting either home made or brought my pond is 13ft by 9ft so it is quite large any advice will be gratefully received thanks
wizard - 6-Mar-15 @ 7:42 PM
I have a pond, which the past two weeks as started to have a green scum appearing on the surface. It appears small but clings together and creates larger area's. We have cleaned it out bydraining and filling at the same but still reappears time. PLease help.
suzie - 22-Sep-14 @ 6:25 PM
I have a goldfish in my garden pond whose body is round like ball with a head and tail coming off. I've had it a number of years and it came like this. It's still growing in size. It swims around fine and eats well. It seems healthy. It lives with another goldfish and 2 koi who are all 'normal' and healthy looking. Any ideas please?
Ros - 23-Jul-14 @ 2:55 PM
my pond is 6ftx4ft and 3ft deep how big pump do i need filterbox and uv many thanx todd
t - 15-Jul-14 @ 5:55 PM
@queenie. How big is your pond? And how powerful a pump do you have? That might help us to help you with an answer.
PondExpert - 16-Jun-14 @ 12:51 PM
why is my pond water cloudty ,however the water from my pump is lovely and clear . any ideas thanks
queenie - 13-Jun-14 @ 3:15 PM
I have a 500gal pond with about 20 medium sizes goldfish, shubunkins and comets, I stopped feeding them at beginning of November. one larger gold fish has been for three weeks, head down in the water with tail and swollen abdomen out. she can swim for short time but cant sink down. I worry she may become frozen to the surface and die. I have tried an infection treatment recommended by my local stockist but its not working, please help,
kevin - 8-Dec-13 @ 12:19 PM
We have lots of baby fish (tiny) and I would like to know the best way I can keep them. I have isolated them from the big fish and most seem to be surviving but for a few.I have ordered a heat pump in the hope they will survive through the winter months but would be grateful for some advice on the best way to help them through the colder months.Any advice would be greatly appreciated. Many thanks. Warwick Gunter
war - 19-Oct-13 @ 11:12 AM
Have had a clear fish pond for 3 years, I clean it out every year before I put pump and filter on every year this year it the water is very brown and not clear though it was before I cleaned it out. I check and clean my filters regulary,any advice why
Denis Brough - 28-Apr-13 @ 2:12 PM
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