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How to Clean a pond

A goldfish or koi pond is a great addition to any backyard. But if it isn’t properly maintained or cleaned it can quickly become an eyesore. 

Depending upon how filthy your pond is you may be able to get by with a little tidying up or you may need to do a full cleanout. If the water is dark in color and has developed a layer of crud at the bottom you may need to opt for the latter. 

In this article, I will be detailing how to do a full pond clean-out. If you decide this isn’t necessary check out this article on cleaning your pond without draining the water. 

How To Clean A Pond Step By Step

  1. Gather Needed Tools & Supplies
  2. Drain The Pond & Remove Fish
  3. Clean Pond
  4. Clean & Inspect Equipment
  5. Inspect Pond For Problems
  6. Fill With Water & Add Fish

woman holding pond weeds over dirty pond

The Best Time To Clean Your Pond

The ideal time to do a full pond cleaning is in the spring. This should be early spring before the water temperature in the pond rises above 55° F or 13° C

At this time, your fish and other bacterial life are in a state of relative dormancy. This is important because cleaning during this period will have the least amount of impact. Not only will it be easier on your fish but also on the biological balance in the pond.

As the temperatures rise in the spring and summer the beneficial bacteria begin to grow and multiply. Cleaning during this time will have a larger impact and throw off the nitrogen cycle. This can result in ammonia spikes in the pond. 

Gather Needed Tools & Supplies

Before you begin the cleaning process you need to make sure you have all the necessary equipment on hand. 

Recommended Pond Clean Out Tools & Supplies

  • Cleanout pump & hose 
  • Pressure washer or high-pressure garden hose nozzle
  • Nets – skimmer net & fishnet
  • Fish Holding Tank(s) – 200 gallons or more with aeration recommended
  • Pond Vacuum
  • Water Treatments – water conditioner, beneficial bacteria
  • Garden Shears – to trim plants

Drain The Pond & Remove Fish

Draining your pond completely can take several minutes or hours depending upon size. Cleaning may begin if you choose while draining is ongoing as the pond becomes exposed. 

Pond Draining Steps

  1. Place the sump or cleanout pump in the deepest spot of the pond
  2. Begin draining your pond water into the fish holding tank 
  3. Drain the remaining water to an appropriate place
  4. After 1 foot of water is removed begin netting your fish and moving them to the tank

First, fill your fish holding tanks with your pond water. Doing this will ensure your fish aren’t shocked by being placed directly into new water. We will go over the steps to acclimate your fish to the new pond water later. 

Make sure your holding tank is in a shady place if possible. You should also add some bubblers for aeration and a net over the top to prevent jumping.  

Put a little thought into where you want to drain your pond. This murky pond water contains a lot of nutrients so you may want to use it to water your garden. If you choose to drain the water into your lawn you should move the hose 2 or 3 times to prevent flooding any particular spot. 

Once the water is low enough to easily net your fish you may begin to do so. As you catch the fish this is a great time to give them a quick look for any disease or injuries. Look for sores, damaged fins, or anything else that seems off. 

Cleaning the Pond 

woman cleaning a backyard pond with a pressure washer

Pond Cleaning Steps

  1. Skim floating debris out with a pond net as the water drains
  2. Wash liner, rock, gravel, and other surfaces with a pressure washer or garden hose
  3. Periodically flush dirty water out with cleanout pump
  4. Use a pond vacuum to clean out hard to remove sludge

While you are draining your pond, get your skimmer net and remove any debris floating around. You can also clean and inspect water features and skimmers as they become exposed. 

With the water drained completely you can now begin to wash the inside of the pond. You can use either a pressure washer or a high-pressure garden hose nozzle. 

Pressure washers work great but you need to use them carefully. You want to keep the nozzle at least 8 inches away from any surface you are cleaning. The purpose of this is twofold. If held too close you risk blowing a hole through your pond liner. Additionally, every surface in your pond has a biofilm on it. This biofilm is the beneficial bacteria that recycle ammonia resulting from fish waste and organic matter in your pond. So we don’t want to wash all of it away.

While washing you will want to occasionally run your cleanout pump to flush the muck out. You can also use a pond vacuum to get rid of any hard to remove sludge at the bottom. 

Clean & Inspect Pond Equipment

With the water drained and the pond cleaned, we can turn our attention to the pond filter (skimmer), pump, waterfall, and any other pond equipment. 

Cleaning out your pond filter (skimmer)

  1. Remove any filter pads and media. 
  2. Gently rinse these to remove any loose debris. 
  3. Clean out any algae, debris, and sludge from inside the filter housing with a pressure washer or garden hose. 

With everything cleaned you can reassemble your skimmer and reattach the pump. 

This process will be the same with a bio falls waterfall if you have one of those as well. 

Inspect Pond For Problems

With everything cleaned it’s a good idea to do a quick inspection before you refill the pond. It’s far easier to tackle any problems when the pond is empty rather than full!

This is a great time to look for things like:

  • Tears or damage to the liner
  • Broken equipment or materials
  • Out of place rocks or other decorations
  • Plants that need care or trimming

Fill With Water & Add Fish

Long lived Koi in pond

Now that the hard work is all done we just need to add water and fish right? Not so fast!

While koi, goldfish, and other pond fish are generally hardy species we want to perform this step with some care. 

Filling the pond and adding fish

  1. Fill the pond with fresh water
  2. Treat water with a pond detoxifier
  3. Add Beneficial bacteria
  4. Acclimate fish to new water
  5. Gently release fish back into the pond

Once the pond has been refilled we will need to treat the water. Tap water contains things like chlorine and fluoride which can be harmful to your fish. This water will need to be treated to neutralize these chemicals. Any commercial pond detoxifier can be used to accomplish this task. You can also opt to add beneficial bacteria at this point. 

Next, we need to acclimate our fish to the new pond water. The water fresh from your tap is likely colder than the water in your holding tanks. Dropping them straight in would stress and possibly shock your fish. 

There are a couple of ways to prepare your fish for reintroduction. 

If your fish are small enough you can place them in 5-gallon pails filled from the holding tank. Place these buckets into the pond and let them float. Leave them there for at least 15 minutes splashing fresh water in occasionally. 

After at least 15 minutes has passed, the water temperature in the buckets should have stabilized. You may now release your fish back into the pond. 

Alternatively, you can replace some of the water from the holding tank with fresh cold water. Simply drain about 25% of the old water and replace it with fresh water. Do this a few different times giving them some time to acclimate to the new water. When you are satisfied with this you may release them back into the pond. 

Final Thoughts

You should now have a nice, clean, backyard fish pond to enjoy! With a few basic tools and a little know-how cleaning out a pond is something anyone can do. 

If you run into any serious problems along the way or don’t feel comfortable with the process, reach out to a professional pond service.