Why Do Pond Fish Die?

Ornamental fish such as koi or goldfish can make a great addition to your garden pond. Like many other pond keepers (including myself) your fish probably provide many hours of joy and entertainment.

Therefore, when you have a sudden death of a much loved pond fish it can be distressing and possibly an indication of a wider problem. This article aims to explain some potential reasons as to why your pond fish might have died.

The 5 main reasons as to why your pond fish might have died are as follows:

• Water quality
• Water temperature
• Overcrowding or overfeeding
• Algae
• Disease

Reason 1 – Water Quality

If you notice that your fish in your pond are dying prematurely then the first thing that you need to do is check the quality of the water. If you have low oxygen levels or high ammonia or nitrate levels, then this can create a lot of problems for your pond. This can result in the death of your fish if left untreated.

If your pond has low oxygen levels then you may notice that your fish are staying nearer the surface of the water, especially during early morning or they may have reduced appetites. Having good quality water and maintaining oxygen levels in the pond are the most important factors to ensure you have a healthy pond.

If the ammonia or nitrate levels are too high in your pond, do not panic there are things you can do to help fix this problem. You can get an ammonia or nitrate level testing kits to help restore the balance in your pond. Or if the levels are too high, it is recommended that you change at least 30 percent of the water to freshen up your pond.

When looking at the levels in your pond, there are recommended levels that you should keep your pond at. The pH levels in your pond should be between 7.0 and 9.0. You should also make sure that your ammonia levels are at 0 whilst your nitrate levels should be less than 50 parts per million. If any of these levels are too high, this can result in devastating effects for your fish.

It is important to regularly check the levels if you want your fish to live in a healthy environment. Although if you have a pond filter that is regularly maintained, this should not be a problem.

Reason 2 – Water Temperature

Another reason that your pond fish could be dying is because of the water temperature. If your pond faces sudden or severe change in its water temperature, then this can cause stress on the fish which in turn can result in death.

Also, if your fish become stressed then they can become more susceptible to certain diseases. This stress can also lead to your fish not handling changes in the water like low oxygen or increased ammonia levels. This is because their bodies are spending more time trying to adjust to the temperature changes than being able to fight anything bad off.

When the weather changes to winter, it is fairly normal for one or two fish to die, but if you notice a significant number of fish dying, then this is where problems can arise. It is a known fact that fish who spend a lot of time in heated up water have a shorter lifespan.

Reason 3 – Overcrowding or Overfeeding

Overcrowding and overfeeding are very common reasons that your fish could be dying prematurely. This combination can be deadly because it reduces the amount of oxygen that is available in the water.

Overfeeding can also be a problem as if the food is left in the water this can break down which releases ammonia and nitrates into the water. To prevent overfeeding it is recommended that you net out any food left in the water after 5 minutes of your fish feeding.

Overcrowding can be a serious problem as this will cause the amount of waste to rise which could lead to ammonia and nitrate levels increasing. This can become fatal to fish if left untreated. If there are too many fish in your pond, then the fish may not get enough oxygen, and this is essential for the fish to survive.

Before your fish start to die, there could be a tell-tale sign that your fish are not getting enough oxygen because of overcrowding. If you suddenly see your fish jumping out of the water, they could be doing this to get more oxygen. If you do notice this, then it is best to check the oxygen levels in the water.

Furthermore, if you do have too many fish in your pond then the water will not be able to break up the bacteria as quickly. This is because there will be too much fish waste for the filter or pump to work effectively.

You do need to closely monitor the population of your fish or if you are overfeeding them as this is not something that can be fixed overnight. However, a good start would be to remove some of the fish, the water balance should then slowly start to resolve itself. However, ensuring your pond has a filter can help to minimise the problems that built up waste can cause.

Reason 4 – Algae

Another reason why your fish may be dying more frequently in your pond is if you have excessive algae growth. If algae is left to manifest in your pond, then it can end up releasing toxins and harsh nutrients into the water that can be very harmful to fish.

Algae starts to grow in your pond as a by-product of the process of photosynthesis as algae creates oxygen during daylight and during the night, algae uses the oxygen that it creates. This can create problems for the fish. This is because if the algae is using up all the oxygen, then there will not be enough left for the fish. If fish do not have enough oxygen, then this will lead to death.

Treating algae can be simple, it is best to first scoop out as much as you can and then use a treatment or remover to clear the rest. You should not do this too quickly though. If large amounts of algae are left to die and decompose then this can release further toxins into the water which depletes the oxygen from the water.

Reason 5 – Disease

Lastly, disease could be another factor as to why you are finding your fish dead. If your fish are stressed then this will reduce their abilities to fight off diseases. So, keeping your fish calm and happy as much as possible is ideal. There are many signs of fish disease that you can look out for within in your pond.

The signs of fish disease could include things like abnormal swimming, reduced appetite, erratic motion, sores, blisters, spots, bulging eyes, discolouration of scales or body, and growths on the body. If you notice any of these from your fish, then you should seek professional advice on how best to help. It is highly important to keep the pond clean and well filtered, and this should reduce the chance of disease.

If you notice some of your fish are acting strange, do not panic, there are treatments that you can put into your pond to try and reduce the disease from spreading. If you do not know what disease your fish have, then you can get a generalised disease treatment. Although if you know that they have diseases like Whitespot or Fungus then you can get treatment or medication tailored to this.

In order to accurately apply the treatment, you need to know the volume of your pond water, so you do not give too much or too little. Also, it is advised that you turn off the UV light. When using specific treatments for your pond it is important that you follow the guidance and use for the full duration.

Conclusion

To conclude, there could be many reasons as to why your fish are dying prematurely. There are however many simple things you can do to help to prevent early death in your fish.

The five main reasons that you fish may be dying young is the water quality, water temperature, overcrowding or overfeeding, algae and disease. These factors can be easily maintained and easy to fix, but if they are left unchecked then it can cause devastating effects on your fish.

The best way to maintain a healthy pond and prevent your fish from dying is to ensure that you have a well-maintained water filter and that you clean your pond out regularly.