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Garden Pond FAQ

We get many questions sent to us regarding both pond construction and water quality, so we’ve put a selection of the most frequently asked questions into a single post to help you find the information you’re looking for and become a pond keeping expert. Don’t forget, if you can’t find the answer to your question here, you can send us a message via the contact us page or give us a call on 01642 612419 – we’ll be happy to provide advice to point you in the right direction. Just click on the question below to jump to that particular section:


Pond liner vs pre-formed ponds | Common water problems & solutions

How to calculate pond liner | How to keep your water clear

How to calculate pond volume | Do I need pond aeration?

Which pond plants do you need? | How to repair a pond



Pond Construction


Pond liner vs pre-formed ponds


So you’ve decided to add a pond to your garden, but you’re unsure whether to opt for a pond constructed from pond liner or a pre-formed pond. Both have their pro’s and con’s and you should make your decision based on three things – your budget, your creativity and how much labour you’re willing to invest on the project.


Pond liners undoubtedly offer the most flexibility during pond construction, as they allow you to shape your pond however you see fit, however this comes at a cost; they require more planning and aren’t the easiest option to install. As ridges and shelves within a pond are essential to simulate natural pond formation, and also help with your livestock’s development, these need to be added manually during excavation at the correct depth – hence the extra planning and labour time. This being said, pond liners allow you to be as creative as you like, require very little maintenance once installed and can be considerably cheaper than pre-formed ponds.


Pre-formed ponds on the other hand are a great option for those who are happy with a static shape pond – as getting creative here is out of the question – and are looking for an easier install option. This doesn’t mean you’re completely restricted on the look of your pond, as everything from rectangular to more naturally-shaped ponds are available, and once they’re installed into the excavation hole and decorated, they’ll look the same as any other pond. Pre-formed ponds do tend to be a little more expensive than pond liner, but with this option you’re saving time on both planning and installing; as the shelves and ridges are also integrated in the preformed shell.



How to calculate pond liner


Unlike pre-formed ponds, you’ll need to calculate how much pond liner you’ll need to comfortably fit your excavation hole. We’re in the process of developing a pond liner calculator to make things easier for you, but in the meantime you can follow the simple instructions below:



Liner length = Pond length + (2 x maximum depth) + 50cm minimum overlap.

Liner width = Pond width + (2 x maximum depth) + 50cm minimum overlap.


Important tip: Purchasing pond liner and only discovering it’s too small when it comes to installation wastes time, money and causes headaches! We’d always recommend buying more than you need by at least 10% – any that’s left over you can use for constructing waterfalls or water features.



How to calculate pond volume


Knowing the approximate volume of your pond helps make choosing everything from adequate pumps and filters to the amount of fish you can stock a lot easier, so it’s a good idea to calculate this in the planning stages. As with the pond liner calculator, we have a pond volume calculator in development, but can use these simple calculations below in the meantime.


For a rectangular pond:








In Metres: Width x Length x Average Depth x 1000
(eg. 2.1m x 3m x 0.6m x 1000 = 3780 Litres)



For a circular pond:











In Metres: Radius x Radius x 3.146 x Average Depth x 1000
(eg. 1.2m x 1.2m x 3.146 x 0.6m x 1000 = 2718 Litres)




For an oval pond:










In Metres: (A x B) x 3.146 x Average Depth x 1000
(eg. (1.2m x 1.9m) x 3.146 x 0.6m x 1000 = 4303 Litres)




Which pond plants do you need?


Plants are an essential addition to your garden pond; not just for appearance, but they also play an important role in creating and maintaining a healthy pond ecosystem and it’s nitrification cycle. Ammonia is naturally present in fish waste which is converted into nitrates by your biological filtration system. These nitrates are then absorbed by the plants and foliage within your pond – allowing for improved water quality. If you’ve ever experienced an algae bloom in your pond, this is often caused by increased levels of nitrates in your water; meaning it’s about time to add some more plants. Depending on where you’re placing the plant will determine which type to go for, so we’ll take a look at the most common plants used in the UK.




If you’re looking for plants to place around the shallow edges of your pond, known as the marginal area, then choosing a fast growing marginal plant such as Mimulus helps hide your pond’s border and flowers in the summer to add colour. Remember you don’t want to restrict the view of your pond, so taller marginal varieties such as Iris should be placed at the back of the pond.





The deeper areas of your pond can often appear bare, so adding Water Lilies – perhaps the most well-known pond plant – add interest to a particular area and add splashes of colour with their beautiful flowers. However, we wouldn’t recommend Water Lilies in Koi ponds as they have a habit of de-rooting them and causing a mess in the pond.





Oxygenating plants play the most important role in your pond, as they help to naturally oxygenate the water – improving water quality and reducing the risk of algae buildup. Elodea Crispa is by far the most common in UK ponds, and they add much-needed oxygen during the day. However, don’t add too many bunches as they also release carbon dioxide back into the water during the night. Many oxygenating plants are notorious for growing quickly, so make sure you prune them on a regular basis to prevent them from growing out of control.


Lastly, floating plants can create a shadowy hiding spot for your fish and also require minimal maintenance. Species such as Water Soldiers and Water Lettuce look great in garden ponds. However, most of these floating plants originate from much warmer climates, so they’re only suitable during the summer months and should be moved to indoors when the temperature falls.


How to repair a pond


Over the lifespan of a garden pond, it’s inevitable that you’re going to have to carry out repairs at some point. Whilst the development of new materials and improvements in pond construction have drastically improved the reliability of both the pond itself and the equipment used, they’re still susceptible to failure. However, pond repair is often very simple and you don’t need to call a professional to do the work for you – meaning DIY repairs are often cheap!



For ponds that are constructed using pond liner, this liner is prone to crack or tear along the folds; especially if natural rocks are used for decoration. In this case, a simple liner repair patch and underwater sealer will quickly and effectively fix the leak. For pre-formed ponds, you can use an underwater sealer to stop a leaking hold or crack instantly.


If the trouble lies with the plumbing in your filtration or pump system, you have a couple of options. You can use self-sealing pipe repair tape as a cost-effective approach to patch leaking pipes or joints or, if you deem the pipe or joint unrepairable, you can easily install a new pipework or fittings to permanently cure the problem.



Water Quality


Maintaining optimum water quality is essential not only for your livestock’s health and wellbeing, but also the appearance of your pond. Whilst this may be tricky during the initial cycle in the pond’s infancy, water quality stabilises as the pond matures and becomes easier to care for; assuming you maintain the pond correctly. However, a sudden change of the chemical balance in your water is not uncommon, so it’s important to understand the most common problems and what their symptoms are. To make things a little easier, take a look at the table below to diagnose your water quality problem and help find a solution:



Symptom Problem Solution
Green Water Algae Bloom Use an environmentally-friendly algae water treatment, such as AlgoRem. Using a UV clarifier will also help.
Rotten Egg Smell High Anaerobic Bacteria (Sludge) Use an effective sludge remover such as Cloverleaf Sludge Answer.
Floating Debris Insufficient Filtration Upgrade your filtration system or install a pond skimmer to remove debris.
White/ Hazy Water Bacterial Bloom This is a natural process for newer ponds. The best solution is to wait to see if it clears over a few days. Otherwise, a UV clarifier can help with more mature ponds.
White Foam Protein Buildup (Spawning) This is often caused by overfeeding or a buildup of fish waste. Adjust feeding or upgrade filtration system. Use a test kit to check chemical balance.
Brown Cloudy Water Dirt In Water This can be caused by bottom-feeding fish. However, it can also be caused by chemical imbalance – so use a test kit to be sure.
High pH (Over 8.5) Too Alkaline Look for external factors which could have caused the rise such as concrete or limestone. Remove these and carry out a 25% water change using a Dechlorinator.
Low pH (Under 7.0) Too Acidic Use a pH stabiliser such as Koi Care Pond Buffer Up.
Positive Ammonia Test Inadequate Biological Filtration Introduce beneficial bacteria to the pond, such as Pure Pond, to help control ammonia levels.
Positive Nitrate Test Nitrobacter Bacteria Not Established As with ammonia, Pure Pond can also be used to keep nitrate levels under control.
Thick Surface Algae Blanket Weed Use an appropriate blanket weed water treatment. The Goodbye Blanket Weed is an easy-to-use option.
Rock Algae (Strands) String Algae Remove as much string algae by hand as possible. Then treat water with an anti-algae treatment such as AlgoRem. Adding more plants to increase oxygen will also help.



How to keep your water clear



Although installing an adequate filter for the volume of your pond will help keep the pond clear, you may experience an increase in algae or cloudiness – ruining the appearance of your pond and becoming potentially hazardous to your fish and plants. The two main problems that prevent water clarity are algae and bacterial bloom – algae being a problem for more mature ponds and bacterial bloom being more common during the infancy of a pond.




Unicellular algae, the main type of algae that causes green water in your pond, can be easily tackled by using a UV clarifier in your filtration system. The UV filter works by exposing the single-celled algae to extreme levels of ultraviolet light – destroying the algae’s DNA and allowing them to clump together as they die. These can then be filtered out by the filter.


During bacterial bloom the water will become hazy; reducing its opacity and making it difficult for fish to find food. Bacterial bloom is more common in young ponds, as it’s caused by a chemical imbalance as your pond establishes a stable ecosystem. Whilst this is a natural process, we’d recommend carrying out a water test to check for any inflated toxic chemical levels to be on the safe side – especially if you have livestock in the pond. The cloudiness should begin to subside within a few days, so give it a week to see if things clear up by themselves.



Do I need pond aeration?


As you know, a pond needs to have sufficient amounts of oxygen to be able to sustain life – that’s pond keeping 101. Knowing how much oxygen your pond needs and how to increase O2 levels if needed comes with experience. For example, if you have a still pond with no equipment to move the water, it’s going to be very difficult to support life. So how do you add oxygen to a pond?


Before we delve into what equipment we can use to aerate your pond, let’s take a brief look at the science behind water aeration. A pond can only absorb oxygen at the surface as it comes into contact with the atmosphere; leaving water at deeper levels depleted of oxygen. Not only that, lower levels of oxygen allow anaerobic bacteria to thrive – causing septic conditions in the bottom of the pond and foul odors at the surface. This is by far ideal for supporting life in your pond. Luckily, adding oxygen is easy and there’s a number of ways to do it.



First off, and this should be a given, you need to have a pump and filter installed that’s capable of producing enough flow for your pond volume. A pump draws the less-oxygenated water from the bottom of the pond and allows it to come into contact with the outer atmosphere by passing it through filter media before flowing back into the pond. In most cases, this populates the water with adequate amounts of oxygen, but there are times when you’ll need to increase aeration further (explained by a little more science)!


The gaseous exchange that occurs at the pond’s surface improves during colder temperatures; meaning more oxygen is absorbed and more harmful gasses are removed. When temperatures start to rise during summer months this process becomes less efficient as the water holds less oxygen and the respiration of your fish increases, meaning more aeration is needed.




So, knowing that water can only absorb oxygen as it comes into contact with the atmosphere, we can decide what equipment to install to increase aeration. One of the most popular options is to install an artificial waterfall. Here, the pump will draw water up from the bottom of the pond up to the top of the waterfall, where the freshly-oxygenated water can run freely back into the pond. You can either create a waterfall yourself with pond liner and decorate with rocks/ plants, or opt for a preformed waterfall for an easier installation.




Alternatively, and perhaps a more traditional option, is to install a water fountain. This can be achieved with a single product, called a fountain pump, which acts as a normal pump but ejects the water through a fountainhead opposed to pumping the water away from the pond.



A third option to increase aeration within a pond is the use of a pond air pump – with our range of Hozelock air pumps being amongst the most popular. Used in conjunction with an airline and air stones, the air pump creates a steady stream of bubbles which diffuse with the water and agitate the ponds surface; increasing both oxygen content and water circulation.


Important tip: During warmer summers you should ideally have two methods of pond aeration installed, as total failure of a single aeration device will only give you a few hours before the health of your fish is seriously compromised.