Spring pond fish maintenance

Springtime is the launch pad for life in the garden. All life in the garden has spent the preceding cold winter months in slumber, resting and recuperating ready to burst into life in spring. The water garden too has been experiencing a period of inactivity and will benefit from some maintenance before the plants, fish and frogs begin to emerge from their winter hideaway.

As the pond water begins to warm up and days lengthen, the ponds appearance will soon be transformed and if we are not careful, we can be caught out by the speed of change, missing our window of opportunity to set the stage for the summer. A useful rule of thumb so as not to disturb the life within your pond, try to carry out any maintenance when the water temperature is cooler than 10oC.

How was the winter?

The work that you need to carry out your pond, preparing it for the spring is largely determined by the severity of the preceding winter and the impact it may have had on the pond. Besides this, there is more standard maintenance that every pond will benefit from at this time, irrespective of the severity of the preceding winter.

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Filters is your filter in perfect condition?


Your ponds water will be at its clearest just before spring, allowing you to see right down to the bottom. This could easily lead us into assuming that the water quality is ideal for the ponds journey into summer. Yet a number of different factors act upon the water over winter that can cause its characteristics to deteriorate. Leaf matter and other organic material that will have invariably found their way into the pond will cause nutrient levels in the water to accumulate, something that may not appear to be a problem when viewing such a clear pond, but these will soon fuel rampant growth of algae as soon as spring like conditions arrive.

Furthermore, if these leaves remain in the pond, their rate of decomposition in the pond will increase over spring and summer, reducing the oxygen content of the pond water. The few months after Christmas, before spring arrives provides us with the ideal opportunity (and water clarity) to remove any settled debris and burdensome silt that may cover the pond bottom. Rather than using a fine mesh net (that will only remove the larger debris and act to stir up the remaining fine silt) hire a pond vac for the day from your aquatic store. While the water is so clear, you can be sure to remove the majority of offending material. As soon as fish become more active and your pump starts to circulate the water, the silt will be stirred up, making it difficult to remove the silt completely (or see the pond bottom!).

Test your pond water.

Testing your pond water at this time will give you a useful guide as to how it may have changed over the months which you have spent wrapped up indoors. The pH can have a tendency to drop close to 7 due to the diluting effect of several months of rain and snow. The pH should be at 8 to be comfortable and this can be achieved by topping your pond up (after vacuuming) with treated tap water which is buffered to be slightly alkaline by the water companies. Another parameter you should check is nitrate because the months of breakdown of organic matter and fish metabolism (all be it very slow) are likely to have lead to an accumulation of nitrates. Test that the level is no higher than 50ppm (using a colorimetric test kit) and if it is, carry out a partial water change with tap water of a lower nitrate. Excessive nitrates promote unsightly algae and blanketweed and should be kept to a minimum.

Preparing you ponds hardware.

The majority of garden ponds are best left unfiltered over the winter, with some pond keepers owning larger ponds preferring to operate at a reduced turnover. For those who have not operated a pump over winter, now is the time to retrieve it from the murky depths (you should have really done this in the autumn and brought it inside). Clean up the exterior of the pump, ensure any pre-filters or straining mechanisms are cleared and that the impellor is clean and free to rotate and that any rubber seals are intact and flexible.

Similarly, remove any larger debris from the primary areas of your filter and clear any settled sludge that will by now have developed quite a stench. The last thing you (and your fish) want is for this putrefying sludge to enter the pond once your turn on your pump. However, be careful not to scrub your filter too energetically as a little grime and slime is very effective for starting up its biological action. Ensure that any filter media (sponges, foams, stones etc) are cleaned using buckets of pond water rather than tap water.

The majority of filter systems fitted in garden ponds now have an integral UV clarifier to keep green water at bay. Unlike a biofilter where the media will remain and be effective for many years, the UV bulb must be replaced each year to keep green water controlled. Spring time is the most logical time to replace the bulb as its hardest work will be in the first 4 or 5 months of the season. Even if your current bulb appears to illuminate, its output will have deteriorated from last season, making it less effective against green water. Fit a new bulb now and you can forget about it for another 12 months.

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Your pond fish will still be blissfully unaware of other life below the ponds surface at this stage, as their metabolism is governed by the ponds temperature. Even though they will not have eaten for months, their energy requirement will have been so low that they will have easily existed on their bodies reserves. The period leading up to spring is a risky time for your fish as they will be at their weakest point and susceptible to attack from opportunistic pathogenic organisms such as bacteria, parasites, viruses and fungi. Your fish will not require food until the water temperature rises to 8-10oC and only then in small amounts. Be sure to only offer your fish what they will eat in 5 minutes, removing any uneaten food immediately. Just as your fish are waking from their refrigerated slumber, so too are your filter bacteria, struggling to break down waste produced by your fish. If your water quality is allowed to deteriorate then your fishes health will be under even greater threat.

Filters can be helped to cope with this years first serving of waste in a number of ways:

1. Add a filter-start bacterial culture to promote the beneficial bacterial action and repopulate a depleted filter.

2. Offer your fish a low protein (approx 20%) diet. They do not require any more than this at low spring and autumn temperatures and they produce far less ammonia when fed low protein diets, reducing the burden on your filter.

Preventative treatment.

Being aware of the heightened threat from disease during these in-between temperatures, we can add a broad-spectrum treatment (usually formalin and malachite green-based solutions) to reduce the population of these disease-causing pests. A repeated dose at the correct temperature can prove to be very supportive to your fish until their immune system becomes more effective in warmer temperatures. For the rest of the year, healthy fish are well able to protect themselves from disease.

Preparing a pond for the spring and summer seasons can be achieved in a single weekend and is useful in both determining how your pond has faired through the winter and invaluable in setting it up for a vibrant and healthy growing season. So go on, get stuck in, the waters really not that cold and your fish will thrive and thank you for it!

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