Spring Koi Pond Maintenance Check List (Cleaning Tips)

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Spring Cleaning a Fish Pond? A Guide to Spring Koi Pond Maintenance (updated)

koi spring pond maintenance
Spring maintenance is important if you want a healthy ecosystem come summer, and even more important if you have fish! Public domain.

As ponds slowly warm, ice thaws, and fish become more active, you just know Spring is around the corner – but is your pond properly prepared for the seasonal change?

Surprisingly, the amount of maintenance and “spring cleaning” required in ponds is largely influenced by the amount of maintenance carried out before and during winter. In-fact, winterization is one of the most important aspects of preparing a pond for spring, and will help ensure your fish and ecosystem have the best kick-start to the new year. Keeping your pond healthy over winter when fish are most vulnerable is important so they’re strong come warmer weather when they start eating again.

Likewise, cleaning up debris and sludge build-up in early winter keeps harmful substance levels lower over the season as beneficial bacteria slow down in colder conditions. Basically, not much really happens over winter if you have taken steps to winterize your pond, and come spring-time, you should have a fairly easy time with cleaning!

Not wintering a pond, or leaving a large amount of debris over winter, can leads to all sorts of issues come warmer weather. Low oxygen content, sick fish (parasites), anaerobic bacteria build-up  (rotten egg smell), and black sludge, are all issues that can lead to a pretty miserable spring clean-up.

Luckily, no matter the state of your pond, there are still steps you can take to get things healthy again ready for summer. Included below is our personal check-list for ponds in spring to ensure the best start to the season and to promote healthy fish throughout the rest of the year.

When should I start cleaning my koi pond?

cleaning koi pond spring
Cleaning and maintenance should start as soon as the pond thaws and fish become more active. Public domain.

As mentioned above, preparing for spring should technically be started in the preceding autumn and winter months. Following our winter care guide will make sure there is much less work to be done in spring and fish are healthy and strong over the season.

However, even if you have carried out all winterization steps (or haven’t), there will still be a certain amount of work to be done as temperatures begin to rise. Firstly, and a very important rule to spring care, is to never begin cleaning a pond if there is still ice on the surface water. Likewise, you should never try to manually remove the ice on the water or try to speed up its thawing process with physical tools. Ice on a pond basically means it’s still in “winter-mode”, so there is little for you to do but wait until the climate gets warmer. There is no set month for spring maintenance, and even in mid-spring some years it may still be too cold to start turning on equipment and feeding fish. Although all pond keepers like to do things differently, we personally recommend taking into account two points to determine if winter is truly over for your ecosystem:

  1. Is there still ice on the pond? If so, wait until it thaws naturally before you start any cleaning.
  2. Is the water temperature below 50ºF (10°c)? If so, wait until water temps rise and fish become more active before feeding. This can be monitored with a pond thermometer.

Once ice has thawed and water temperatures begin to rise above 50ºF (10°c), you should start to see your fish becoming slightly more active – this is when you should start your spring koi pond maintenance routine! At this point equipment can be started again, heaters removed, debris cleaned, beneficial bacteria topped up, and fish feed slowly added in relation with temperature.

Spring Koi Pond Maintenance Check-list

Note: If you’ve done a good job wintering your koi pond some of these steps may not apply to you, such as cleaning bottom sludge. The list below is a comprehensive one which includes everything that should be considered, so you can simply pick and choose the steps that apply to you!

Step 1: Remove Heaters & Switch-On Equipment

de-icers for fish ponds
De-icers work to keep a hole in the ice over winter, but can be removed as the pond thaws in spring.

If you’ve been running a de-icer or heater over winter you’ll eventually want to remove it to save on electricity and allow the pond to achieve a more natural temperature balance. De-icers are designed to keep a hole in the surface ice open for gas exchange to take place, so the best time to remove them would be when your pond thaws and temperatures rise. Heaters, on the other hand, are used to maintain a more constant water temperature – taking the edge off winter and providing extra warmth in spring. Whether to remove a pond heater will depend on your circumstance, as they’re especially useful for breeders wanting to pack on weight to their koi early in the year. If you’d like to run your heater longer so you can start feeding sooner, you can do this for the first month of spring without issue (just be sure to switch it off by summer!).

After removing your de-icer, it’s time to also switch on any pond equipment that was off during the winter season. Not all of us will have switched off our pumps and filters, but for those in the coldest areas, it’s often best practice to protect equipment from internal damage ice damage. You can safely switch on pond pumps again when your water is free from morning ice, although they can be turned on sooner if the frost is only minor as the flow should keep them from freezing up. Before switching on pumps, you’ll want to drain your filter box of any sludge build-up and make sure the media is free of debris. Over winter and without the flow of water (oxygen), beneficial bacteria in filters will die and you’ll end up with smelly gunk from anaerobic bacteria which should be cleaned before the pumps are on. Fountains and waterfalls can also be turned on as they’ll help keep top ice away and provide extra aeration for beneficial bacteria and fish.

Step 2: Clean Out Excess Sludge and Debris

clean out ponds in spring
Pond vacs are fast and efficient tools for cleaning sludge and muck from the pond floor.

An important aspect of preparing a koi pond for winter is performing a big clean out of debris and sludge which often accumulates in large quantities during autumn. If you managed to get most of your autumn debris from the pond in the previous year, there likely isn’t much left to clean come spring. In-fact, we’d recommend not cleaning out small amounts of sludge that may have been left behind as they will provide your beneficial bacteria a good source of ammonia (their food) to begin re-colonization. Once temperatures slowly rise and oxygen and food sources increase, beneficial bacteria will begin growing in numbers and will keep on top of the waste naturally.

However, if you missed the autumn/winter clean-up, you’ll definitely want to remove some of the muck, especially if it’s black in color. Debris left in the pond over winter will decompose much slower than in warmer months, and if there is also lack of oxygen content, you’ll have a really smelly problem come spring. In low-oxygen conditions anaerobic bacteria thrive and consume sludge at a much slower rate, eventually producing a potent smell of hydrogen sulfide as a by-product – the distinct smell of rotten eggs! If you have large amounts of muck in spring, or small amounts of black sludge, you’ll want to remove this with a pond vacuum to prevent it mixing with upper layers of water. We recommend a vacuum cleaner as it’s faster, easier, and much more efficient at removing muck and stopping it leeching throughout the pond. As well as removing excess muck, you can start up any skimmer box you have in place and install your pond netting to prevent fallen debris and springtime predators.

Step 3: Treat Fish for Parasites & Possible Infections

treat fish for parasites in spring
If you have fish in your pond, treating for parasites in winter and spring can help prevent infection.

If you have fish in your pond, especially koi, you should treat the pond for both parasites and external bacterial infections in winter and spring. During colder weather a kois bodily functions slow down, including their metabolism and immune system. This is why koi and other pond fish eat less during winter, and also why they’re the most vulnerable to parasites and infection during this time. To prevent parasites making your fish sick, you should treat your pond before winter as part of the winterization process, and then again in spring to ensure they’re parasite-free as they come out of hibernation (or, more accurately, torpor).

The most common parasites are often flukes (skin/gill) and internal worms, but luckily both can easily be treated with a broad spectrum parasite killer. In most cases, we usually recommend praziquantel, which can be found in Aqua Meds Aqua Pazi treatment for ponds. This parasite treatment is safe for fish and the ecosystem when dosed correctly, and will quickly eliminate both internal and external parasites. It can be dosed as part of your winter maintenance routine in late autumn, and again in spring when fish start to become more active and begin feeding.

Although less common, bacterial infections can also be treated if you notice any wounds or injuries on your fish. External parasites, such as flukes, can cause nasty sores on the skin of fish which easily become a breeding ground for bacteria. Likewise, a pond which has been iced over all season can lead to fish becoming injured on any fragmented ice; especially around heaters. Since pond water is usually very clear in colder months, you should be able to spot any injury fairly easily. If some of your fish are showing signs of problems, we recommend treating the pond with a natural healing agent and anti-bacterial product to prevent infection. For this, API Pond’s Melafix is a good choice.

Step 4: Install a UV Clarifier for Algae

UV clarifiers clean algae in ponds
UV clarifiers are great for combating free-swimming algae, and will also reduce harmful bacteria which is helpful in colder weather.

The best time to start combating algae is early spring, as this is when the nuisance weeds likes to get a foothold in preparation for summer.  To grow successfully algae requires two things – sunlight and nutrients. By cleaning out any excess sludge in winter and spring algae will have less nutrients to establish itself, but it will still be able to grow slowly in the presence of sunlight. To prevent full algae blooms in summer and to get better water clarity year-round we recommend installing a UV clarifier as part of your spring maintenance routine. Fitting a clarifier early ensures that less free-swimming algae spores aren’t able to lay dormant and bloom in the warmer months to come. Clarifiers are 100% safe for fish, and destroy algae at the cellular level as a pump passes water through the specialized UV chamber of the equipment. They’re particularly useful for koi ponds as they also reduce the amount of free-swimming harmful bacteria which can lead to fish sickness (useful in colder weather), but won’t harm beneficial bacteria as the majority lives on the pond liner and within the filter media.

For the best results a UV clarifier can be installed as soon as you turn on your pump after winter, and can be combined with a natural algae deterrent for maximum algae prevention.

Step 5: Supplement with Beneficial Bacteria (And Oxygen)

Beneficial bacteria supplements can be added in spring when temperatures rise to help kick-start biological filtration.

After cleaning out excess muck and making sure filters and equipment are in good order, you can consider topping up the pond system with extra beneficial bacteria. This step should only be carried out when you have water flow from your pump and waste is under control, as beneficial bacteria require high oxygen conditions to thrive. Adding bacteria too early in the year, especially if there is still ice on the pond, would likely kill most of the population as there is little aeration and gas exchange taking place. You also should not add bacteria when you have problems with excess waste, as they’re likely only going to worsen the problems and contribute to the waste levels themselves.

Once things are in order, you can add a concentrated beneficial bacteria product to the pond to help kick-start the spring population and improve biological filtration. As beneficial bacteria work better in warmer temperatures, we recommend adding them when pond temperatures start to rise above 50ºF (10°c). To further improve their efficiency, you can also add a dedicated aerator to provide direct oxygen to the eco-system. Not only will this ensure beneficial bacteria have a surplus of oxygen to breakdown harmful substances, it also makes fish (especially koi) more comfortable and less stressed.

Step 6: Slowly Increase Fish Feeding

koi spring feeding
You can start feeding fish as they become more active, but feeding should be monitored to prevent wastage.

Finally, as water temperatures rise, koi and goldfish will start to become more active as their metabolisms start to boot up after winter. Although it can be temping to start feeding as soon as ice thaws, you should wait until your fish are properly active and you’ve finished the rest of the spring chores. This isn’t because food will rot in the stomachs of a hibernating fish (an untrue myth!), but because providing food which goes uneaten contributes to waste and spikes in ammonia; especially in low oxygen conditions. It’s important to get your water filtration and waste levels in good standing before adding more potential waste to the system!

Monitoring water temperature can be useful in determining when to start feeding fish, although we prefer a more physical approach by simply taking note of the behaviour being presented. Koi are smart animals and will only eat when they’re ready, which usually shows in their behaviour as they start swimming slowly along the pond liner. This behaviour is a good indicator of when to begin feeding, as they’re now likely searching for food on the bottom of their environment. Once you notice koi are more active, we recommend feeding small portions and monitoring daily feeding to ensure all food is being taken. If some is going to waste, reduce the amount until temperatures rise. If all food is gone, increase the dosage until there is a little waste.

The type of feed is personal preference so long as it’s high in protein, healthy fats, and has a wide vitamin & mineral profile. If you’ve been feeding wheatgerm food until now, you can continue that until mid-spring when temperatures rise further. if you’d like to pack on extra weight early in the year, switching to a high quality summer feed is also a fine option!

10 thoughts on “Spring Koi Pond Maintenance Check List (Cleaning Tips)”

  1. If my koi and goldfish are still in their “hibernation” mode, can I move them out of my pond so I can fully drain the pond and clean out the inches of leaves and needles at the bottom? I understand that I need to correctly re-acclimate them.

    New pond-owner here. Did not “winterize” as I should have and definitely learned my lesson for next winter.

    • Hi Emily,

      Moving fish when they’re in torpor can be very stressful, so unless your water quality is suffering, I’d say just try to wait out the cold weather and perform a deep clean alongside a few larger water changes when it warms up.

      In your situation, I’d first perform a water quality test and check ammonia, nitrites, nitrates and pH levels. If these are all within safe parameters, or close to, I’d wait until the pond warms and fish become a little more active. After that, I’d vacuum/rake out (rake is messier) the bottom gunk and perform a nice big water change (40-50% – remember to de-chlorinate!) immediately afterwards to improve clarity, replenish alkalinity, and reduce overall nitrogen compounds. Then, I’d continue to perform 10-20% water changes weekly until water quality is good and then maybe pull it back to 10-20% biweekly, depending on fish stocks.

      If you’d prefer to remove fish and drain the entire pond, then yes, still try to wait out for warmer weather as it’ll be extra stressful if they’re still “hibernating”. If your water quality is particularly bad, such as a very high ammonia reading, then cleaning sooner may be necessary as this can be more dangerous than the stress of moving them. Just make 100% sure that the new environment you intend to move them to is the same temperature as the pond water they’re in, as temperature shock can kill fish instantly.

      In either case, after you have performed a water quality test you should have an idea of what you’re working with!

      Here are some links which may also be helpful:


      Do let me know if you have any more questions or would like further advice. Happy to help where I can!

    • Hi Jo,

      Unfortunately, we do not. We’re purely a web-based resource. However, I can highly recommend installing something on your computer/phone/tablet called f.lux. It’s an application that filters out blue light, but you can adjust it to whatever setting you need so that your screen isn’t so glaring on your eyes! I use f.lux every night when I write on my laptop and it has helped tremendously with not getting headaches or as much eye strain. It’s also a free app. Hope this helps! And please continue reading, as we greatly appreciate all of our readers!

  2. Hi! So much good ,positive information. Thank you very much. I purchased 6 inch Butterfly Koi last year for the first time through the mail. For the most part a positive experience EXCEPT for the parasites that came with them. After back to back monitored PP treatments just before Winter 2019-20, I winterized, shut down the pump and continued running the bar aerators in shallow end of 40 foot long pond. I winterized as you suggest,drained and filled with clean water my biologic strap-media filled waterfall and cleaned my skimmer,filter as well. Then I started everything up and have been running ponds since ice-out here in Western MA roughly March 23. Water is crystal clear. Everything looks good. Now…last year 2019 after my six 20 inch Koi spawned in my upper pond in June and soon after adding 10 new parasitic infected butterfly koi in my lower pond, I noticed a real decrease in the appetite of the 6 big boys in the upper pond. This continued from the spawn til’ Winter shut down the pond. They don’t appear undernourished. Their skin is clear. Could their appetite loss be attributed to eating all the eggs from the spawned female. I have about 50 babies left from winter all looking good with only 2 losses from big pond I immediately removed from upper pond and they were 2 inch babies. I’m hoping after the PP treatments late last Fall and good pond maintenance ALL my Koi will have good appetites soon. Any suggestions from you and observations after my long explanation of my lack of hunger dilemma much appreciated! Thanks Very Much, Herb Johnson

  3. Thanks for the great tips for Preparing Your Koi Pond For Spring. Spring brings with it an abundance of new life in the garden and a desire to spend more time outside. If you have a pond, you will have more fun enjoying the view of your garden.


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