How to Care for Pond Fish: Our Complete Guide

Caring for pond fish, like any fish keeping, requires you to follow the basics. If you do this, then there is every chance you will have great levels of success. Our complete guide shows you how you can create a safe, healthy and visually pleasing fish pond with our favourite, reputable products.


Managing water in a fish pond

Cleaning your fish pond

Specifications for a fish pond

Pond fish care, maintenance and behaviours

Feeding your pond fish

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Managing water in a fish pond

The most important thing to remember when keeping pond fish is ensuring that the quality of your water is fantastic. At this point, it is worth mentioning that water clarity (i.e. how clear your water is) is for your eyes only, as the fish are not bothered by this. You can have green murky water which is of fantastic quality, and you can have crystal clear water which is of poor quality. Ideally, we will have water which is of both good clarity and good quality.

When we are talking about good quality water, we mean:

  • A stable pH (i.e. how acidic or alkaline something is) of pH 7-8
  • Negligible levels of Ammonia (NH3) – i.e. 0
  • Negligible levels of Nitrite (NO3) – i.e. 0
  • Good levels of water hardness (GH and KH) of 120 degrees General Hardness

You can test for the various parameters above that are required in a pond by using a test kit by NT labs.

In order to achieve the above, your pond should firstly be established. When we say established, we mean that it should’ve gone through the nitrogen cycle during the pond’s infancy. For more information on this topic, read our blog on the nitrogen cycle.

Once established, the pond is a balanced ecosystem that will have levels of good bacteria (Nitrobacter and Nitrosomonas) in the filter designed to handle fish waste by converting any ammonia/nitrite produced by the fish into harmless, dissolved gas. It is imperative that you look after the good bacteria in your filter as these will in turn look after your fish.

In order to do this, NEVER clean your filter media (sponges) in chlorinated tap water. When conducting a filter clean, this should be done in old pond water – you are not looking for the media to be pristine, but instead just ‘quite clean’. You can also help the bacteria by dosing the filter with of the following pond biological enhancers:


Water Hardness

The next thing you will need to manage in your pond is the water hardness. GH or ‘General Hardness’ refers to the dissolved levels of magnesium and calcium ions in the water, while KH or ‘Carbonate Hardness’ refers to the measure of carbonates and bicarbonates dissolved in the water.

Naturally occurring water in the form of streams, rivers, ponds and lakes is rarely purified in a distilled water sense. Instead, it is packed full of dissolved salts, buffers and nutrients, and the levels of these will vary according to geography and local conditions. Fish of all types worldwide have evolved over millions of years to inhabit very specific water conditions, and it is our job as pond keepers to try and replicate these conditions in order to keep the fish happy and healthy.


Water pH levels

GH and KH are often intertwined with pH (a scale used to specify how acidic or alkaline a water-based solution is), which is another measurable factor in water chemistry, equally important to fish health. A pH of 7 is considered to be neutral, while a pH below 7 is considered acidic and a pH above 7 are alkaline. Although pH, GH & KH are separate measurable entities, it is difficult to adjust one parameter without affecting the others.

Rapid changes in pH can stress fish out and be detrimental to fish health. As a result, the pH of your pond should remain relatively consistent and stable. It is important to have a good KH in your pond in order to keep pH stable for your fish. The KH has a buffering capacity to neutralise nitric acid (produced from the nitrogen cycle). Without KH, the water would become naturally acidic over time which could result in fish fatalities.

In areas of the country with hard water, the buffering will be a natural occurrence. Areas of the country (such as Manchester) with soft water, will normally need to introduce KH to their pond or aquarium in order to keep pH consistent. Having suitable levels of GH and KH creates permanent hardness which helps most fish with osmoregulation and other natural bodily functions

If your pond is established, and you have maintained water hardness then in theory your pond water will now be of fantastic quality. In order to keep your pond correctly aerated we would recommend moving the water, either with a waterfall/fountain or install a pond air pump or aeration kit.

If you follow all of the above, you should have great success with your pond. If you do run into any problems, then Complete Koi & Aquatics offers free water checks and fish health checks to all customers coming to the shop. 

Specifications for a fish pond

In our opinion, the minimum requirements for pond size would be around 150 litres (e.g. 100cm X 50cm X 30cm) however, this is only a guide. When keeping fish, it is important to ensure the fish are happy and healthy - this is much easier to achieve in a bigger pond, though we appreciate that not everyone has the space. 

When it comes to pond size, we always recommend going for the largest pond you can fit or afford. Keeping larger volumes of water is often much easier than maintaining small volumes, as parameters tend to be much more stable. When considering pond size, fish species should also be taken into consideration. Keeping goldfish in a 150L pond would be acceptable. On the contrary, keeping Koi Carp in a 150L pond would not be advisable as Koi grow much bigger than goldfish


How many fish should I have in a pond?

This is an extremely difficult question to answer given all fish grow to different sizes, but as a rule of thumb, we would recommend 1 fish per 30 litres (based on common goldfish).

As the fish grow though, this figure will obviously change. The easiest way of understanding a pond's capacity for fish is by testing the water. If you have great water, free of both Ammonia and Nitrite, then it is acceptable to add more fish. Likewise, If you have so much as a hint of Ammonia and Nitrite, then there is a good chance you are overstocked.


Can you put fish straight into a pond?

It is never advisable to put fish immediately into a pond. This also goes for aquariums! Fish should be acclimatised slowly, allowing them time to adjust to changes in water parameters. 


How do I introduce fish to my pond?

As mentioned earlier, fish of ALL types are very sensitive to changes in water parameters. When we introduce fish to a pond, we have to assume that the water parameters from the source will be different to the water parameters in your pond.

In order to make this less stressful for the fish, we start out by simply floating the sealed bag containing the fish in the pond for around 10 minutes. This will alter the temperature of the water inside the bag to match the pond.

Once 10 minutes is up, we suggest cutting the top off the bag and rolling down the sides so the bag is open and floating at the top of the pond. Over the course of around 20-30 minutes, you should introduce small amounts of your pond water into the bag every few minutes. This will in turn, begin to gradually adjust the water parameters in the bag to match your pond water. Once the time is up, it is now time to release the fish. Simply turn the bag inside out so the fish are free and dispose of the used fish bag.


Feeding your pond fish

We can advise on the best products in which to feed your pond fish and how much and how often this should be done. Check out our dedicated blog post on how much you should be feeding your pond fish for more in-depth information.


What to feed pond fish

When it comes to feeding pond fish, seasons matter. In winter, fish are in a form of hibernation and seldom require food. They may take small amounts if the temperature is above or around 8 degrees Celsius however, it is imperative that this is low in protein and easy to digest. If the temperatures fall below 8 degrees Celsius, we would recommend stopping feeding. In order to monitor pond temperatures we would advise using a floating pond thermometer.

During these cooler months we recommend feeding wheatgerm:


As the weather begins to warm up or indeed cool down (i.e early Spring and late Autumn) we can start to introduce small amounts of protein to the fish’s diet. We don’t want to overdo this here, as the fish’s metabolism will be working at a reduced rate however, we need to provide them with some strength coming out of/going into winter. We recommend one of the following feeds for this:


In the warmer months, we will want to greatly increase the fish’s protein uptake, allowing it to grow on, strengthen up and colour up. In order to do this, we recommend one of the following feeds:


When selecting a feed for fish, it is important to review the pellet size. Small fish cannot fit large pellets in their mouth however, large fish can consume small pellets. Therefore, if you have a broad range of fish sizes it is advisable to feed a combination of pellet sizes or simply stick to small pellets.

Sturgeon are slightly different in their behaviour and are not affected by the cold. As a result, they will eat all year round. Sturgeon requires a special sinking feed which is rich in protein and oils:


Learn more about Sturgeon and other types of pond fish in our blog post.


Cleaning your fish pond

We will move on to discussing the best ways in which you can clean your fish pond and ensure that your fish are kept safe and healthy.


How to clean pond water with fish in it

The best way of cleaning pond water is with an adequate pond filtration system. Pond filtration systems use a combination of mechanical and biological filtration media to improve the clarity and quality of pond water.

This should be paired with an adequate UV clarifier in order to eliminate suspended algae cells in the pond, therefore reducing green murky water. In instances where UV clarifiers have not been installed, certain algaecide products can be used, but these should be exercised with caution as they can reduce saturated oxygen levels and damage aquatic life.

If you are struggling with a build up of detritus on the bottom of your pond, you can eradicate this using a completely harmless enzyme based treatment by Cloverleaf known as Sludge Answer. Enzymes in this particular treatment feed on the detritus, gradually removing the build up from the bottom of your pond.

In circumstances where you’re struggling with cloudy water caused by fine particles, a flocculent can be used which causes the suspended particles to clump together, which will ultimately end up in the filter (if being used) or at the bottom of the pond. At all times of the year, it is advisable to remove any visible debris such as leaves, using a simple garden net.


How to remove algae from a pond without harming the fish


In a fish pond, there are two distinct types of algae:


Suspended Algae (Green Water) i.e. phytoplankton

Suspended algae causes green water in a pond. Green water is completely harmless to aquatic life however, many people want to get rid of this so that they can see their fish. The best way of eliminating suspended algae is by installing a UV clarifier. UV clarifiers work in conjunction with a pond pump – as the pond water moves through the UV clarifier, the ultraviolet rays destroy the plant's cellular wall, eliminating the phytoplankton which will then be removed by your filtration system. 

In ponds without UV clarifiers, algaecide products can be used to eliminate green water however, these are chemical treatments and should be used cautiously. Quite often, these products will strip the pond of oxygen so when using, combine with a waterfall or pond aeration kit and never use on a hot day.


String Algae (i.e. Blanket Weed)

String algae/blanket weed is a form of algae which adheres to the sides of a pond, resembling long waves of green hair. As string algae is not suspended in the pond, a UV clarifier cannot remove it. String algae is great in harbouring aquatic food such as water louse, but unfortunately can quickly overrun a pond. We would recommend manually removing the blanket weed as and when you see it with a pond net or rake.

Alternatively, you can use an enzyme-based product which is perfectly safe for aquatic life in eliminating blanket weed. In our opinion, Blanket Answer by Cloverleaf is the best product on the market for this and is incredibly fast acting and efficient.


Can pond fish survive without a pump or filter?

Wild ponds do not have pumps, filters or aerations systems and yet contain fish, so how is this possible? In garden ponds, we generally create oxygen in the water by creating turbulence however, plants can also do this. Oxygenating plants such as Hornwort (Ceratophyllum demersum) photosynthesise in the same way as terrestrial plants. In doing so, they consume Carbon Dioxide (CO2) and convert this into oxygen which living organisms breathe. Therefore, if you’re looking to create a wild natural pond lacking in mechanical instruments such as pumps, it is imperative that you add oxygenating plants.

The oxygen produced by the plants will also stop the water stagnating. Pond fish such as Goldfish and Tench are ideally suited to such ponds as they are adapted to living in these environments. Of course, if you’re looking to create a pond without a filtration system, you cannot expect good water clarity or large fish volumes however, it will most likely serve as a brilliant resource for local nature.


Pond fish care, maintenance and behaviours

Here we discuss some of the main questions asked surrounding the care of pond fish and their notable behaviours.


When do pond fish breed/spawn?

Pond fish in the UK tend to breed/spawn as the weather warms, typically May-June. Prior to spawning, fish may exhibit semi-aggressive behaviour, chasing each other around the pond frantically. When fish spawn, you can expect the water quality to degrade, along with the water clarity getting murky. Quite often, there will be a foamy slick on top of the water which will quickly end up in the filter. During spawning, avoid trying to treat the water in any way and allow the process to continue naturally without interference. This is a short-lived event and conditions will return to normal fairly quickly.

After spawning, fish can often be tired and in some instances may have small wounds or blemishes. It is important at this point to ensure that your water quality returns and that you keep an eye on any fish which could have problems. If any wounds start to look sore and redden, we recommend treating the pond with salt or an anti-bacterial acriflavine treatment.

Not all ponds can expect their fish to spawn. Fish will only spawn if the conditions are absolutely correct. On top of this, the chances of rearing the fry to adults are relatively slim. The odds are stacked against them as they are an extremely nutritious snack for a variety of aquatic life (including their own parents!).


When do pond fish hibernate?

Pond fish will typically hibernate during the colder months (e.g. December – Feb), when the pond temperatures fall below 8 degrees Celsius. During this time, pond fish will typically drop towards the bottom of the pond and will be largely inactive. During the winter months, it is important to make sure that the pond surface does not completely freeze over as this can halt vital gaseous exchange, effectively suffocating the fish.


What is eating my pond fish?

Pond fish unfortunately have plenty of natural predators in the UK. The most common of these the Grey Heron, although

  • Cats
  • Foxes
  • Mink
  • Otters
  • Cormorants
  • Goosanders
  • Grass snakes
  • Gulls
  • Crows

...also pose a threat (to name a few).

If you want to stop fish predation in your pond, there are several steps that you can take. The first of these is positioning a decoy deterrent around the pond. This normally comes in the form of a life-sized fake of one of the predators in the list above; quite often this will be a plastic heron. Predators often like to feed alone and can get skittish around others. Having a potential competitor around a pond may stop others coming to feed.

Installing a garden pond net or grid over your pond will restrict large predators from getting into the pond. This is a sure-fire way of stopping the likes of herons and cormorants from taking any fish. The best and most visually appealing way of deterring any pond predators is by installing a garden pond electric fence around your pond. These are incredibly safe and highly effective products which will deliver any potential predators a short sharp shock should they choose to venture close to your beloved fish pond.


Contact Us

We hope that we have covered all the questions you may have had on pond fish and how you can effectively care for them. If you have any alternative questions or concerns, please contact us or alternatively, come down to our store and have a chat with our team of experts. We are always willing and happy to help at Complete Koi & Aquatics!

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