Autumn koi pond maintenance

As autumn approaches, our pond enters its last scene her before the final curtain of winter approaches. Even at this late stage, the story could still have two endings, either as a tragedy or with the ponds players living on happily ever after.

Everything in the garden is starting to wind down after this summer’s busy period of growth and colour. Days start to shorten and the temperature starts to fall as the calendar seems to accelerate towards Christmas. If we are not careful, we will be caught out as we instinctively start to spend shorter periods in the garden as our days shorten, and may run out of time for everything we need to accomplish with our pond. Just as there is a collection of seasonal jobs to carry out in the garden, there are certain things every responsible pond keeper should start to do as autumn approaches. Fear not, as there is still plenty of time if you start thinking and acting now, but leave it any longer and the British weather might well have the last laugh, bringing the first cold snap or out of the blue, paying little notice of our globes warming climate.

Your fish are still likely to be feeding in September, and it is their last opportunity to feed, digest and make full use of a higher protein diet. This will allow your fish to continue to grow as well as to store excess energy that they will consume as reserves through their on coming winter. Be prepared to respond to the weather, by offering your fish a lower protein diet when the of water really starts to cool off. This may start in August, or as late as the last days of September, so keep a check on your pond temperature by using a floating pond thermometer. When the water drops below 14 degrees C and looks as though it has done so for good, wean your fish on to a lighter diet.

Your fish will quite happily, and eagerly continue to accept a high protein diet as the water cools, but being cold-blooded will not require such a high energy levels in their diet. For your pond’s sake, and to keep on top of your water quality, change to a lower protein diet (approx 20%) that will accommodate your fish’s requirements and keep waste and water pollution to a minimum. Keep some low protein food in stock from August, just in case autumn falls upon us sooner than we anticipate.

As your fish approach their season for hibernation, your fish will experience a period of limbo in a temperature no-man’s land. This period represents the most risky time for your pond fish, perhaps even drifting in and out of activity several times, and being aware of this, you should try and make their entry into hibernation as seamless as possible.

Autumn Water Quality

If you have managed to keep on top of your water quality through the growth season, your filtration will still have quite naturally led to an accumulation of by-products that really need addressing prior to the winter. Nitrates and dissolved organic compounds (those that discolour the water) that have entered your pond through food and planting should be diluted away through water changes prior to your fishes autumnal inactivity. A simple nitrate test will tell you whether you need to carry out a restorative water change, anything at 50 ppm or greater (as highlighted by your Test Kit) needs improving with a series a small water changes. There last thing you want is for your fish to be stewing in an organic and inorganic soup throughout the winter months.

By the end of September, your pond plants too will have enjoyed their best growing period, starting to die back with their foliage starting to brown off at the edges. Watch out that these plants don’t contribute too much to the organic content of your pond by breaking down in your pond water. Compared to a larger more natural pond your, garden pond is relatively small and if it is planted heavily around its perimeter, it will be subject to more organic debris than a larger pond relative to your ponds volume.

Just as these plants appear to be able to predict the forthcoming cooling off period as autumn approaches, the onset of autumn does not come as a surprise for your fish either.

If your pond contains goldfish, koi, orfe, shubunkins, or Rudd in any variety, being relatives of the carp family have a physiology that is geared to overwintering. In fact, experiences in breeding these fish clearly point to these fish requiring a cold period as part of their breeding calendar. For weeks, they will have been taking their cues from the ever decreasing day length, and the gradual decline in water temperature. Their physiology will respond to these cues by preparing themselves for a fallow period, storing energy. For thousands of years, this successful family of fish have survived winter periods quite safely. However, being ornamental variants of their wild-type ancestors, they are not as hardy and will benefit from your helping hand into winter. When Mother Nature would ruthlessly select out those weaker fish over winter we want our weaker hand selected ornamental fish to reach spring successfully. The biggest threat to their welfare over this period is probably disease.

It may come as a surprise to learn that winter poses little threat of disease to your pond fish, as the cold water renders pathogenic organisms such as bacteria, fungi and parasites inactive in a similar way to fish. Problems do occur or though over the August to September period (depending on the temperature) when your pond fish are winding down in line with your pond’s water temperature, but the density of pathogens is still sufficiently high to pose a threat. This is why we should do all we can to introduce our fish to their period of hibernation as seamlessly as possible. If the water temperature hovers too long between 6 degrees C and 10 degrees C, then our fish will be more prone to succumbing to disease, being unable to mount a concerted defence as the activity of their immune system becomes seriously affected.

Problems may not manifest themselves this side of winter, with infections and health compromises festering unchallenged in a latent state only to flare up next spring when water temperatures start to rise. It is only then that these opportunistic micro-organisms are likely to gain a foothold on your fish whose immune system tends to lag as the water warms.

What can we do?

By managing poor water quality as best as we can as discussed earlier, we can minimise our fishes’ stress levels and reduce their susceptibility to these ever-present disease-causing organisms. We can also adopt a more proactive approach by dosing the pond but the broad spectrum course of treatments to reduce the density and therefore the threat of these pathogens. If a pond is treated late enough, it is possible to reduce the density of pathogens by not giving them long enough to re-multiply again before the onset of winter.

The main threat to all of our pondfish in these limbo periods of autumn and spring is from bacteria and fungi. Those of your fish with long and fancy fins are more prone to attack as the cold water over winter curtails the blood flow to their bodily extremities, causing tissue to die in localised areas inviting bacterial or fungal attack. Any abrasions or sores that may have not healed completely will also be liable to attack from fungi, leading to your fish appearing to grow a cotton-wool like coating in localised areas of their body.

In either case of fungal or bacterial infections, their likelihood can be reduced by a prophylactic or preventative dosing in the autumn (and later on in the spring) with the malachite or Acriflavine-based pond treatment. These medications can be used to treat affected fish either in situ in the pond or in a more concentrated bath on an individual basis. The extent to which your fish’s body tissue is at risk from disease can also be reduced by providing your fish with deep water in which they can spend the winter. A depth of at least 2 ft,( and preferably 3 ft) should be the minimum in which your fish are overwintered. The deeper the better.

Even though our fish’s well-being over winter is largely at the mercy of the elements, good preparation of our fish and their pond, starting in August will have a positive influence on our fish. We can then rewrite the script for our fish as they approach winter, ensuring they are all present and correct when the curtain rises again in spring.

Kill blanketweed and string algae.