How to clean a garden pond

Inspired by a popular garden pond guide. This walk-through is based on the comprehensive YouTube video "How to deep clean a garden pond! Everything you need to do and know!", which covers every stage of the process from draining right through to refilling. It is thorough and well-paced — worth watching before you start if this is your first full pond clean.

1. Pick the right time of year

Early spring — March or April — is ideal for a full pond clean. Fish are still sluggish from winter, which makes them easier to catch, and you avoid disturbing breeding amphibians that arrive later in the season.

Avoid cleaning in midsummer if you have frogs or newts present, and never clean in winter. The cold slows everything down, the fish are at their most vulnerable, and you will make a miserable job of it.

2. Gather everything you need first

You will need: a submersible pump or bucket to remove the water, a large container (a paddling pool works perfectly) for temporary fish storage, a net for catching fish, pond dechlorinator, a stiff brush, and a pond vacuum or wet-and-dry vacuum for sludge. Have a bucket of pond water ready too — do not put fish straight into fresh tap water.

3. Catch and move any fish

Fill your temporary container with pond water — a mix of the existing water and some fresh dechlorinated tap water. Use a fine net to catch fish carefully. Work slowly and avoid chasing them for long periods; keep them in a shaded spot and do not leave them unattended.

Move any large pond plants to the same container to keep moisture around their roots. Smaller wildlife — snails, pond skaters, larvae — will mostly find their own way back when the water is replaced.

4. Pump or bail the water out

A submersible pump makes short work of this. Drop it into the pond, run the hose to a drain or onto the garden (the nutrient-rich water makes excellent plant food), and let it run until the pump starts to cavitate.

At that point, bail the remaining few inches by hand. This is where you will find most of the accumulated sludge — do not be surprised by quite how much there is.

5. Remove the sludge

Scoop out the thick black sludge from the base with a spade, trowel, or pond vacuum. Transfer it to a compost heap or spread it thinly on a garden border. It is excellent for the soil, though it does smell.

Leave a small amount of sludge in the pond if you can — it contains beneficial bacteria that help re-establish the pond's ecosystem quickly. Do not aim for a sterile concrete bowl. That said, if the sludge is very deep, getting most of it out is the priority.

6. Scrub the pond walls gently

Use a stiff brush and fresh water to scrub algae and blanketweed from the pond walls and shelves. You do not need any cleaning product — plain water is safer for the pond's ecology when it refills.

Do not pressure wash a lined pond. The jet can damage or shift a flexible butyl liner. Firm scrubbing is perfectly adequate.

7. Service the pump and filter

Take this opportunity to clean the pump thoroughly. Rinse the foam cartridges in a bucket of pond water — never tap water, which kills the beneficial bacteria inside. Check the impeller for debris, and inspect the cable for any damage before putting it back in the pond.

Clean UV clarifier bulbs if the filter has one, and check that the lamp itself still works. They have a limited lifespan and often need replacing each season.

8. Refill with dechlorinated water

Run fresh tap water in slowly, using a hose set to a gentle flow rather than blasting it in at full pressure. Add pond dechlorinator (also called water conditioner) as the pond fills — tap water contains chlorine and chloramines that are toxic to fish.

Let the temperature of the fresh water equalise with the water in the temporary fish container before moving to the next step. This takes a couple of hours at least.

9. Return fish and plants gradually

Float the container holding your fish on the pond surface for 15 to 20 minutes so the temperatures equalise properly. Then gently tip the container to let the fish swim out at their own pace. Do not net them a second time unless you absolutely have to.

Replace plants on their correct shelves, trim any dead growth, and add a dose of beneficial bacteria product to help the biological filter re-establish quickly. The water may go a little cloudy for a few days — that is completely normal.

When to call a handyman

A pond clean is a satisfying DIY job, but if the liner is torn, a fitting has started leaking, or the electrics on the pump feel dodgy, those are jobs to get sorted properly. Richard can help with outdoor electrical connections, pond fitting repairs, and general garden maintenance across Sandwich and East Kent.