Top tips from our friends at Tetra on how to maintain a pond after winter

When the days become warmer and sunnier and new green shoots start to appear, we know that spring has sprung. But how are the pet fish in your garden pond doing? With the support of our friends at Tetra, we are taking a look at what kind of spring care you can do for your pond fish.

Caring for your pond fish during colder months

The cold winter temperatures mean that your fish’s immune system is not particularly active, but you should ensure that they are still fed over winter, providing that they are responsive to food. If the water temperature is below 10°C, you should feed your fish with wheatgerm-based feeds that are easy to digest and particularly good for the fish, as their metabolism is only starting up slowly. Make sure to only feed your fish small amounts to ensure that no food residues remain in the pond. Once the water temperature goes back up above 10°C, you can switch back to feeding your fish standard foods. This kind of feeding helps your fish stay fit and healthy for the best possible start to the new pond year.

Most pond fish, especially koi carp, have a natural ‘problem’: the rate of their immune system function is inversely related to water temperature. As the fish also have to draw on their own resources to survive the winter, they will no longer be as fit and healthy by the time spring rolls around. This makes them more susceptible to diseases when the water temperatures rise again. Correct autumnal conditioning and offering winter feeds is therefore the best way to help your fish stay fit and healthy in preparation for spring.

Leaving your fish in garden ponds during winter

If you leave your fish in an outdoor pond during winter, it’s a good time to check your fish stock when they start to become active again. It’s also a good time to get an idea of the maintenance measures you need to conduct in and around the pond in the near future. These can include pond plant care measures, checking the water quality and scheduling partial water changes. Don’t forget to also check the technical equipment e.g. possible frost damage to the filter, perished O-rings etc.

Reactivating your pond filter

When the water temperature increases, the time has come to reactivate your pond filter. As you should have cleaned the filter before winter began, by the time spring comes around all you need to do is check its electrical functions, add the filter substrate and restart the filter. Please note, however, that biological filtration will not be instantly fully effective, as the still cool temperatures mean that the filter bacteria need longer to settle on the substrate and become active.

Checking the water parameters

Your fish’s health primarily depends on the water quality. As such, you should regularly test the water parameters in your pond. It is particularly important to regularly check the ammonia and nitrite levels in early spring, as you will have started to feed your fish more and biological filtration only takes effect gradually. Ammonia and nitrite levels should both be undetectable in the pond.

You should also check the other key water parameters, such as the carbonate hardness and pH-value. If critical limits are reached, a major partial water change must be conducted as a matter of urgency.

Are partial water changes necessary?

Irrespective of any partial water changes you conduct due to poor water chemistry parameters, you should also conduct a larger one in spring at the latest – think of it as your fish spring clean. No matter how well you prepare your pond in autumn, the water quality will still always deteriorate over the winter months. Larger (e.g. 25%) partial water changes are therefore not only an important pond care measure for spring but also the best way to kick off a new and successful pond year.

Fish diseases in spring

Pond fish are particularly susceptible to disease in the spring. Ectoparasitic and bacterial infections are especially common. You should therefore closely examine and monitor your fish so that you can respond to problems quickly, if necessary, and in line with professional advice. Warning signals include fish remaining listless after the water temperature has risen, fish with wounds or inflamed areas on their skin or fins, a grey slimy covering over the skin and fins and gasping at the water surface.

You also need to take action quickly if you notice white spots or cotton-wool-like fungal growths on your fish’s skin and fins. Specialist retailers can provide appropriate and effective medicines that are well tolerated by fish and should be used in line with their instructions. Please note, however, that even the very best of medicines cannot help your fish in the long run if they are not offered the best possible environment through the use of appropriate care measures.

“Your fish’s health primarily depends on the water quality. As such, you should regularly test the water parameters in your pond.”
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