These days, fully draining a pond in order to clean it is not usually necessary and should only be considered a last resort.
A common misconception is that old water requires removing before the pond can be thoroughly cleaned. But not all mature water is bad quality water, in fact the opposite is often true with the water being full of micro-organisms including good bacteria which help to keep the ecosystem of the pond in balance. Removing the pond water will mean that you are also removing the beneficial bacteria which break down harmful fish wastes and make the water safe for aquatic life. So wherever possible, it is best to retain as much mature pond water as you can in order to maintain the population of micro-organisms.
Topping up after draining can cause even more disturbance to the balance if tap water is used without first dechlorinating it. Chlorine, and chloramine, whilst making tap water safe for us to drink, is toxic to aquatic life and must be removed from the water before exposing them to it. Small water changes - or small top ups where evaporation has occurred - may be beneficial at times, and in these instances we would recommend that you use rainwater (collected in water butts) or tap water that has been treated with a quality dechlorinator.
Cleaning a pond without draining is the least disruptive method when it comes to maintaining a healthy pond, as it allows the majority of the good bacteria to continue providing biological filtration during and after the worst of the waste is removed.
The best times for cleaning the pond are at the start of spring and during the autumn. A small spring clean carried out when the water temperature starts to rise (and the fish become more active) can be very worthwhile. We would recommend a quick check of the filter, removal of any floating debris, the thinning out of pond plants, and the addition of a pond supplement/tonic to give things a boost.
Then, during mid-late autumn, a more intensive clean can be carried out, as by then amphibians will have long finished breeding and insects such as dragonflies and water beetles will have reached their adult flying stage and can safely move out of the way to other ponds. Also, at this time, most deciduous trees and shrubs will have dropped the majority of their leaves, and these can be netted off the pond before they sink and start to decay. A pond vac will ensure a thorough clean of the bottom and sides of the pond, and the filter should be inspected to see if the mechanical media requires rinsing. These procedures will mean that waste levels are minimal as we move into winter, thus ensuring a more comfortable and safe hibernation period for the fish.
During the intensive pond clean, we would recommend that you firstly remove any floating surface debris such as leaves, twigs, dead insects etc with a pond net. A net that has a wide head and reasonably fine mesh should ensure you are able to skim off all sizes of debris effectively. If the pond is sited in an area where it receives a constant amount of debris (for instance, if it is surrounded by trees), then it would probably be worth investing in a pond skimmer which can be used to collect the debris on an ongoing basis, not allowing any of it to sink and decay on the bottom. Less sludge on the substrate is better for the fish, and also means less work for you when vacuuming. For smaller ponds, floating or submerged skimmers are ideal, and for larger ponds, box skimmers are the most efficient. Unlike nets, skimmers are better long-term investments (particularly on larger ponds or those that become covered with debris easily) as they take all the work out of using a net to keep the surface clear, and remove finer debris that nets may miss.
The next step is to remove the unpleasant sludge that has accumulated on the bottom of the pond. Although you don't need to remove every last bit, it is best to remove as much as possible to keep the nitrate level down (which in turn causes algae) and to ensure your fish have a safer hibernation period in the lower reaches of the pond.
For smaller ponds, treatments such as AquaPond Care Sludge Control can be used to help eliminate sludge. This product introduces specific types of bacteria to the pond which consume sludge without deoxygenating the pond, and it is not harmful to fish, plants, or other wildlife.
Larger ponds, however, will need a more heavy-duty approach. In years gone by, pond keepers will have used a simple net or rake, gauntlet gloves, and copious amounts of elbow grease to remove pond sludge. However, this method is extremely laborious and messy and often involves draining of the pond. Pond vacs (pond vacuum cleaners) have made this job much easier, less unpleasant, and nowhere near as time consuming. Pond vacs operate in much the same way as a regular, household vacuum cleaner; except that these work with water and pond debris rather than air and household dirt. Most models are placed at the side of the pond, on dry land, and a telescopic pipe used to reach the bottom and sides of the pond. As you manoeuvre the vacuum head slowly back and forth over the substrate, the pond vac will pull water from the pond, at the same time sucking up the sludge. Most vacs will come with a selection of cleaning heads to tackle hard-to-reach areas of the pond and to deal with different types of debris. There is no need to drain the pond beforehand, and the fish can remain in situ whilst cleaning is carried out, as they instinctively know to move away from the equipment. Different models work in a variety of ways but the most common type are set up to dispose of the removed water and muck straight down the drain (or onto a garden plant border - it is a great fertiliser). Other types trap the sludge in a specialised bag or container, which can then be emptied afterwards, and many also return the 'cleaned' water to the pond. For smaller ponds, the hose-powered models are ideal, and for larger, deeper ponds, use a pump-powered model. Remember that the deeper the pond, the more powerful a vac you will require in order to main good suction at depth. Lastly, never vacuum during the summer period when amphibians and insects are reproducing.
After clearing out the sludge from the bottom of the pond, it is wise to wait a couple of weeks before carrying out maintenance on the pond filter. This is because no matter how carefully our pond cleaning was carried out, some beneficial bacteria may have been lost. So rather than risking losing more at the same time by cleaning the filter simultaneously, it is best to wait a short while, allowing the bacteria to build back up to full levels, before cleaning the filter on a separate day. A well optimised and maintained filter should only need cleaning a few times per year - the amount of cleaning depending largely on your pond's bio-load. In general, filtration should be cleaned as soon as you notice a drop in water flow from the filter outlet pipe, as this would suggest that the mechanical filter media is starting to become clogged with debris. It is likely to become clogged after a thorough pond clean, as everything in the pond will have been stirred up; so following sludge clearance, be sure to watch for any drop in water flow from the filter outlet. Remember that sponges should only ever be rinsed in a bucket of water taken from the pond, in order to preserve the beneficial bacteria that break down the fish waste. Biological media should not require cleaning as often, but when it does, again, a quick rinse in aged pond water is all that is needed. Aside from the impellor, nothing inside the filter needs to be spotlessly clean. After the filter cleaning is complete, consider adding an additive that will give the filter bacteria a boost.
Finally, although algae isn't waste in the broadest sense of the word, it still needs to be controlled so that it doesn't smother plant life, cause water quality issues, or reduce the oxygen level in the pond. Small amounts of algae are natural and beneficial, providing hiding places for fry or insect larvae, and some types will be nibbled at by goldfish. Problems occur when algae is left to grow uncontrolled, where it rapidly spreads and takes over the entire pond. If the algae ends up smothering the pond plants, these will die back, sink to the bottom and create more sludge. At the same time, the oxygen level in the pond will drastically reduce as bacteria work to break down this extra waste, meaning that your fish will struggle. It is not necessary to drain a pond to remove algae. A pond vac will make short work of string algae, and a UV clarifier can be installed to tackle the free-swimming algae (green water). Algae may also be controlled longer term by adding more pond plants, as these will compete with the algae for the nutrients in the water, which in turn will slow algae growth.
If you have any questions on pond maintenance, please speak to a friendly member of staff. Your nearest branch of Maidenhead Aquatics may be found here.
With spring well and truly in the air, pond sections are starting to buzz. Display ponds are appearing and this year we’re focusing on wildlife in many of our stores, as well as the fishes which are always the stars of the show. It’s not all about the great outdoors though, and some very exciting captive-bred marine fish are causing a stir, as well as some nicely settled tropical fishes following a busy winter season of imports.
Fishkeeper Fry 2022 has now come to a close and it has been a real joy to have been able to deliver this year’s programme, particularly having lost a year due to Covid restrictions. Our schools have produced some amazing work with the support of their fantastic teachers and we’re thrilled to see the way in which the children have engaged with the tasks and activities throughout.