How to clean, reduce and remove pond sludge
Sludge is ok in natural wildlife ponds but in ponds containing fish, pond sludge can lower oxygen levels and encourage algae growth.
A lined fish pond shouldn’t have any detritus on the bottom, dealt with by a combination of pond filtration and maintenance. And if unfiltered the pond sludge will have to come out before the pond pump and filter go in, as otherwise, they will just block within hours.
Remove sludge with a pond net
If the bottom material is made up of leaves and organic matter you may be able to net it out. Use a coarse net with a strong handle and draw it across the base of the pond until it's clear. If small particles are left behind in the water draw a finer net through the midwater, removing as much as you can. Remove pond sludge by hand and you can make sure you don't harm any aquatic life.
Suck out pond sludge
If there are silt, mud, dead algae, fish food and fish waste on the bottom of the pond the best tool to use is a pond vacuum cleaner. Specially designed for ponds, a pond vacuum enabling hoovering like you would your carpets, but instead, you draw it slowly across the base of the pond. The vacuum fills up with pond sludge and dirty water before discharging through a drain hose at the back.
Pond vacuums are the most hassle-free way of removing dirt from the bottom of the pond and if you’re worried that they will suck up something small and living, fit a sludge bag or detritus collector to the waste hose. Vacuum your pond regularly and your water will be healthier too.
Filter to prevent pond sludge
After you’ve netted and vacuumed, a solids handling pump connected to a pond filter is then used to control detritus build-up long term. Ponds should be designed so that all waste collects at the deepest point, and that’s where the pump should go. Solids handling pumps can deal with large solid waste and don’t have foam inside the cage, so they shouldn’t need regular maintenance. Their job is to pick up the waste and pump it to the filter at the side of the pond where you can deal with it, and remove it.
If the pond doesn’t have one deep spot the pump can be moved around the pond over several days and weeks to best remove detritus. Some pumps have the option of fitting another inlet, enabling suction and solids removal from two different places.
Is a box filter or a pressure filter best for a dirty pond?
In really dirty ponds, pressure filters can block frequently, reducing in flow and performance, and this is their main criticism by users. If you have to choose a pressure filter for other practical reasons, choose one with a cleaning device and flush capacity to offer ease of cleaning. If you want a filter that you can leave for long periods without cleaning then fit the largest black box filter you can. With a huge surface area of sponge and a bypass, they don’t block very often and if they do, water flow is not reduced.
Ask yourself why the pond is getting dirty? If you have lots of large fish and are feeding heavily then a koi filter is the order of the day. Koi filters are designed to cope with large amounts of solid and biological waste, and allow easy cleaning and drain functions to allow you to flush to waste. And if you want true hands-off, regular cleaning choose a filter that cleans itself automatically.
Use Sludge busters to reduce pond sludge
There are lots of products available to help you and your filter deal with waste and create a healthy pond. Beneficial aerobic bacteria can help to reduce and liquefy sludge, clearing the water, and making it easier for your filter to remove. No aerobic bacteria is a substitute for proper filtration however and the two work best in combination.
How to prevent pond sludge
The worst sludge occurs in heavily planted ponds that are overgrown and haven’t been maintained in years. They’re the ones that will need elbow grease to physically remove as much waste as you can, even before vacuuming. To prevent pond sludge build up make sure that submerged plants are properly potted and dressed with aquatic gravel to keep the soil in. Tie pond plants in winter to ensure they don’t blow over and spill soil, and cut off all brown, dead leaves as you spot them.
A pond cover net protects your pond from predators like herons but also from leaves and organic matter from getting into the water and breaking down. Fitting a pond skimmer will also remove waste while it is still floating before it sinks and breaks down.
Always leave sludge at the water’s edge on the day you remove to enable any pond life to slither back in. Once they’re gone it makes great compost and garden fertilizer.