Regular Maintenance for your Garden Pond

Some of the tasks listed here may seem obvious to you but my experience is that they are not so obvious to all. So forgive me if you think that I am overstating matters.

Leaves        Silt        Blanket Weed        Algae       
Filter        Plants        Evaporation        Frogs       
Water Testing       


First, the pond itself. It is important to ensure that any vegetation that doesn't belong in the pond is removed. If you have trees or large bushes near your pond, you will have a constant supply of leaves to remove. Not too bad a task for most of the year but can be a bit of an effort in the autumn.

There are two main reasons for this, apart from making the pond look a mess. Firstly, leaves and other non-pond vegetation that have been in the water for even just a few days start to decay and the gasses given off by the decaying process are harmful to the fish. A few leaves in the summer won't hurt, but in the autumn there are many more leaves. If this sort of debris is left in the pond and the pond freezes over, the gases given off during the decaying process will be trapped in the water and the fish are likely to die, or at least get extremely stressed which, in turn, makes them susceptible to other diseases.

Secondly, once in the water, the leaves will inevitably migrate towards your pump and although they are unlikely to be sucked into the pump, they will clog the input to the pump, thereby reducing the flow of water around your system and in extreme cases if the pump isn't pumping enough water, it will overheat and get badly damaged. The same is true for your UV filter.

As well as non-pond rubbish, you need to note the condition of your pond plants. Lilies constantly replace their leaves and flower buds and the dying ones must also be removed periodically along with any other dead pond vegetation. I usually get into my pond every couple of weeks through the summer and remove all dead lily leaves and flowers as its easier than trying to lean into the pond from the edge.   Top


Unless you are very lucky, silt will build up in parts of your pond over a period of time and should be removed before it gets too much. You'll soon get to know which areas of the pond are susceptible to silting up and a fine mesh net will usually suffice for removal, but be aware that if you leave it too long, there will almost certainly be frogs and newts living in the silt, so tackle this job gently. Unfortunately, the pond will be cloudy for some time afterwards but will clear within a couple of hours.   Top

Blanket Weed

A major cause of frustration to pond keepers is blanket weed. It is actually fibrous algae but it looks like weed. As its name implies, if it is given time, it will form a blanket over everything it can grow on, especially your plants. The problem is exacerbated by the fact that the clearer you can get your water through filtration, the more sunlight can penetrate the pond and the better are the conditions for the blanket weed to grow. It is possible to treat the pond with chemicals to restrict its growth but I don't believe in putting anything into the ponds that I don't have to.

Whilst I don't like chemicals, I have now found a product that is almost 100% effective against blanket weed and I use it just once a year in the spring once the water has started to warm up. That product is Cloverleaf Blanket Answer and it is becoming quite widely available in garden centres. I buy mine through the Internet because the prices are usually better. All you need to do is mix the correct amount for you size of pond in a watering can and then pour it into the pond. The pond will turn milky for a couple of days but it will soon clear and the effect on any blanket weed is dramatic.

If you really don't want to use chemicals, the best way to get rid of it is to take a simple garden cane and ensure that its end is smooth and without any spikes that could damage your liner and insert it into the blanket weed and gently rotate the cane between your fingers. You'll find that the weed will begin to wrap itself around the cane and it can be pulled out of the pond. Its better to do this before the blanket weed gets too much of a hold on your ponds because if it gets too well established, you may end up pulling out your plants as well. If you notice that your plants are being pulled out, try to reduce the amount of weed around the stick or start again with a smaller amount.   Top


In only a few weeks, algae can build up on the top of your waterfall to such an extent that it will affect the depth of the water in the pond above. Check regularly to ensure that level doesn't get too close to the top or you will lose water from the top pond and as you are pumping it from the bottom one, you'll run out of water for your fish. There is nothing you can do to prevent the algae from growing but I use an old nail brush to clear the edge of the waterfalls every few weeks to reduce the algae. If you have used Cloverleaf, this will not be a problem.   Top

Pump Inlet Filter

As mentioned, once leaves etc get into the pond, they will tend to migrate towards the pump. Check regularly that the pump inlet is not blocked. I find that I can do this without switching the pump off by lifting it to just below the surface and pulling any debris free from the inlet filter. If you have to take the bottom from the pump for this job, switch the pump off first. Notwithstanding this, you must follow the instructions from the pump manufacturer. DO NOT poke anything into the pump to remove debris whilst the pump is running. You may damage your pump, but as your fingers are going to be wet, you are highly likely to lose control of the probe and if it catches on the pump impeller, it could be flicked into your eyes.

Main Filter

As you will have seen from my pumps and filters pages, the main filter also needs regular maintenance. Any sponges in the filter need to be cleaned every couple of months in the winter and considerably more often in the summer. Once you have got the water clear, if it begins to cloud up, the sponges need to be cleaned. The easiest way is to spray them off with a hose pipe. However, the chlorine in the water won't do your filter any good, so once they have been cleaned, squeeze them out as dry as possible and rinse them in a bucket of water from the pond. The small amount of chemicals left will be dissipated in the volume of the pond and the filter will be OK.Once you get experienced with your pond, you'll be able to detect a slight change in its clarity that a casual observer wouldn't notice. Clean the filter as soon as possible and you'll benefit from the better views of your fish.

As often as necessary but at least twice a year, you will need to remove accumulated silt from the bottom of the filter. This can be a very messy job. If you have left it too long, the silt at the bottom of the filter will be thick, black and pungent. Always use a good quality barrier cream on your hands and wear old clothing. Stains from this stuff don't come out of most materials. The best place for the silt is on the garden, as it seems to be a great fertiliser. However, its strong stuff so spread it around thinly because too much on one plant can be bad for it.

The process is simple. Remove all the contents of the filter, empty the filter, spray it clean with a hose and empty that water away. I bought a waste water sump pump, the sort used to keep cellars from flooding as it is capable of handling the solid debris that will have accumulated in the filter and then I can arrange to pump the waste away to a drain pipe that I have installed next to the filter. The pump wasn't expensive and it saves having to emply the filter by hand if you don't have an inbuilt drain system for your filter. Then replace the contents and refill the filter. If you can achieve this in less than about three hours, your filter will resume work straight away. If it takes much longer than that, the bacteria on the filter medium will have started to die and it will take a few days for the filter to get back to full performance. If the media is out of running water for more than 24 hours, the filter will have to start the process completely and it will be some weeks before it regains full performance. Filter cleaning is not a good job to do in the middle of winter when the water is only just above freezing. However, keep a close eye on your pond water clarity because the first sign of cloudiness means that the filter needs to be cleaned. If you are certain that your filter is working properly but it still can't keep the water clear it may be that you have too many fish in your pond. Consult your local water garden centre for advice because you may need to build a bigger filter.   Top


Pond plants grow at a prodigious rate throughout the warm months of the year and need to be kept in control. The easiest way to do that is to decide how big you want the plant to get and simply rip off any additional growth. These plants usually have roots along their stems so the handfuls that you rip out can usually be planted elsewhere in the pond. In this way, your plant population soon grows. Failing that, just throw it into your compost bin. Don't forget to offer it to your friends though, because they might be throwing out pieces of something that you haven't got and its better for both of you to swap plants than to buy new ones.   Top


During the frog mating season, we have literally dozens of mating pairs of frogs in our ponds. Unfortunately, there are usually a couple of casualties each year. Over amorous males occasionally restrict the breathing of the female and she dies. If you see a frog lying upside down on the bottom of the pond, remove it as soon as possible because they decompose very quickly and will be harmful to your fish.   Top


In the hot months of the year, expect the level of your ponds to drop by at least 2 to 5cm each week. This is due to evaporation and the loss will be greater if you have a large water surface area. If you have a means of collecting rain water, that is ideal for topping up the pond as it doesn't contain the chemicals that are in tap water. Don't worry too much about it if you don't have a water butt. I've never had one and I add about 5 cm to my ponds every couple of weeks if we haven't had any rain. If possible, play the hose into the top of your pond system so that the cold water from the tap can mix, even if only partly, with the circulating pond water, so that the fish won't be subjected to a current of very cold water.   Top

Water Testing

The quality of the water in the pond will determine the health of the fish so its important to check it regularly. Testing kits for the PH levels, Nitrite and amonia are available from all garden centres and should be used according to the instructions on a regular basis. If in doubt, take a jar of your pond water to the garden centre and they will be able to analyse it for you and give advice on what to do to correct any problems.