Garden Pond Guide

Everything you need to know about garden ponds

Pond design and location
Where to build your dream garden pond? It’s all about location location location. Just like your home, your pond should be located where you can enjoy it most. Ideally you should see it from the house, however you must take size, position and condition of the garden into account.

Sunlight and exposure
Partial shade is good for a pond, ideally 4 to 6 hours of direct sunlight per day is also ideal, extended deep water zones help prevent excessive warming of the water and algae formation in areas exposed to a lot of sunlight.

Size
The larger the better, although no pond is too small to be useful, if possible aim for 4 to 5 m² of surface area, this will allow frogs & newts to breed as well as some dragonfly species.
 


Shape
This is not crucial, but probably looks best kept simple. An informal curve shape works well for a wildlife pond. A bog garden of wetland plants on the pond side will greatly increase wildlife visitors.

Depth profile
It is important that the deepest point is a minimum depth of 75 cm. This is recommended to prevent complete freezing in winter, allowing hibernating amphibians and invertebrates to survive the coldest winter when the pond is frozen.

There should be a shelf about 20 to 30 cm for marginal plants also a gently sloping area for use by bathing birds which will warm quickly in sunny weather.

Trees and shrubbery
Deciduous trees and conifers, as well as plants that develop strong roots, should be far enough away from the pond. Root barriers offer protection from plants such as bamboo, which develop strong penetrating roots.

Power and water connection
Proximity of the pond to power and water connections can facilitate operation and control of the devices in and on the pond.

The right pond technology
In addition to selecting the right combination of pump, filter and UVC clarifier, the position of the pump in the pond is important.

A filter pump should be placed as deep as possible so that it can displace pond floor sediment. Fountain pumps are positioned closer to the surface for reduced maintenance.

How to calculate your pond liner size

 
Pond liner installation guide
 

1 Dig the hole to the required shape for the liner, taking care to make the sides sloping rather than vertical. To create planting areas for marginal plants leave steps from 20 cm to 40 cm deep as required (as shown in the illustration). For a perfect finish, ensure that the top edge of the pool is level. This will make edging the pool easier with minimal visible liner exposed.

2 Ensure the pool area is free from sharp stones, place underlay on the base and sides of the excavation and then place the liner in position. Should you need to tread on the liner remove shoes to avoid piercing. Lightly anchor the liner in position with bricks evenly distributed around the edge of the liner, not the excavation.
 
 

 

3 Run water into the pool gradually, at the same time pulling and tucking the liner into shape to ensure a neat finish. You’ll notice that the liner will stretch at first, then as the weight of water increases, it will mould itself to the shape of the sides. Fill the pool completely, checking that the liner fits closely all round. Leave overnight, to ensure proper settlement of the liner. Trim off excess liner around the pool with scissors or a knife, leaving 30cm overlap for anchorage.

 
 

4 After a week you can complete your pool by edging in stone, or paving as desired, allowing for a small overhang to hide the liner from direct sunlight. For a different effect, grass turf can be used, which may overhang and touch the water.


Pre-formed pond installation
This excellent video from TheOutsideLiving shows a detailed build including a watercourse and water feature. The products featured are not the exact items available from B&G but the principals are the same and we stock everything needed to create a pond of this type.
 
Our pre-formed pond range is available HERE
 


Watercourse installation
Slopes for watercourses should be no steeper than 40%
 


Rocks and aggregates
Do not use porous rocks in ponds or watercourses such a sandstone. Harmful elements can be leaked out. Always use hard non porous rock such as granite and slate.

New ponds
When you first fill your new garden pond, record how much water it takes to fill it, as you will need this information for future reference.

When a new garden fishpond is built, it will typically take 4 to 6 weeks for a viable healthy population of nitro bacteria to build up before the bio-filter is working efficiently.

It is therefore wise during this early period to introduce Koi or Goldfish slowly. A continuous supply of oxygen is important to enable the bacteria in the filter to live. The pond filter bacteria need oxygen to convert ammonia to nitrates. Without oxygen the bacteria die quickly within eight hours. Once dead, it takes about five weeks for the colony to reach good viability once more. For the first weeks therefore, do not overfeed fish until the bio-filter is well established.


How to measure pond water volume
An important prerequisite is that you must calculate the volume of your pond as this will determine the size/capacity of all your ancillary pond equipment i.e. filters, pumps, UV clarifiers and aerators.
 
  The diagram above shows a simple way to assess the volume of an irregular shape by breaking it down into smaller sub units.
   
  In this example the pond has been divided in two main sections A and B. Measure each section in feet. All figures should be rounded UP to the nearest whole foot. For filtration purposes you would be better to over estimate the volume. (This only applies to filtration calculations and NOT for medication. It is GOOD to over filter but BAD to over medicate). The volume of each section is calculated using length x width x depth. This gives us an answer in cubic feet. Each cubic foot holds 6¼ gallons of water. The volumes of the two sections (A & B) should then be added together to give the total cubic capacity. This is multiplied by 6.25 to give the total volume in gallons.

Effective pond volume
When selecting the proper size equipment for your pond; actual pond volume alone is not enough, you must determine the effective volume of your pond which is influenced by environmental factors i.e. Is your pond affected by direct exposure to sunlight, shallow depth or climate conditions. If so you may add the following to pond volume.

If average pond water depth is less than 2’6” or 75 cm add 25% as shallow water heats up more and therefore requires more filtration.

Is the pond is located in full sunshine i.e. 6 hours p/d add 25%
or part sunshine 4 - 6 hours add 15%

NOTE: information above does not take into account “fish stocking levels”

Fish stocking densities
An allowance has to be made depending on the kind of fish in your pond e.g. Koi produce more waste than goldfish and therefore require a better filtration system and more attention to detail.

As a rule of thumb: calculate not more than approximately 1 kg of weight of all fish per 1000 litres  of water. At a minimum water depth of 80 cm, Koi require 1.5 m of water depth for safe habitat.
 


Fish and water quality
Always buy the best Koi and Goldfish food you can afford (i.e. high-protein low ASA) as this will give you good water quality (i.e. less pollution) and fish will grow to the optimum size and fitness in your pond. The fish food should be completely consumed in 2 to 3 minutes, fish food that stays on the surface, later sinks and impairs water quality.

Pond chemistry (GH KH)

GH = General water hardness i.e. levels of calcium magnesium and other essential minerals.
‘O’ Hardness = Soft water
KH = Carbonate hardness (or alkaline buffering)

It is important not just for fish health but also for algae growth as well, pond water can vary depending on load, the filtration type and how well the water is managed through the water changes. Consistent water quality is equally, if not more important, than the test results themselves.

Ammonia, nitrates and phosphate should be kept at 0 ppm. Nitrates should be kept under 50 ppm, GH no lower than 100 ppm and KH kept no lower than 50 ppm. A good electrolyte level is maintained by a proper GH which also helps maintain a good redox which in turn aids water clarity and good osmotic function in fish. For long-term health, generally most pond fish like a higher PH of about 7 to 8.

Pond foam
Foam around waterfalls and the water features is not uncommon, however, if this is a permanent problem, there may be other issues at play in your pond.
 
 
Often this is caused by too many organics, solo in your bio load, watching the amount of food you feed and improving filtration can go a long way. Foam can also be caused by excess phosphates.

Chemicals
Do not add chemicals to a pond unless necessary, the absence of a filter is more often the reason why people add chemicals. When chemicals are to be added, it is essential to follow the written instructions and pond volume must be calculated accurately.

Biological pond care products
For sludge buildup, products such as SediFree, are useful in aiding the breakdown of sludge and other organic matter through the action of bacteria and enzymes.

Pond algae
There are hundreds of different types of algae which can cause problems in ponds, from those that are suspended in water, to others which spread across the surface in long fibres.
Algae can lead to deoxygenation of water and have a detrimental effect on pond life.
 


Symptoms
There are many different symptoms depending on the algae present. The most common symptoms:
A “pea soup” caused by fine algae suspended in water.
Floating green scums.
Blanketweed or Silkweed are very common

And algae have dense growths of hair like strands which float under or on the surface, or cling to marginal plants.

The cause of the problem

Most ponds have an algae problem at some time or another, but it thrives where garden ponds are built in a sunny position, with very little planting to provide shade across the surface.

It also forms in nutrient rich water which could be due to:

A build up of organic matter (sludge) on the bottom.
Fertilisers leaking into the pond.
Common pond debris, fish faeces, leaves etc.

Algae can be promoted by using tap water to fill or top up ponds, so ideally use rainwater.

Control
New ponds - sight them with at least part of the pond in slight shade and aim to plant at least one third of the surface with aquatic plants, while ensuring there are also sufficient submerged oxygen generators.

Ideally there should be a minimum pond depth of 75 cm 2.5 ft to prevent water warming up rapidly in sunshine, which speeds up algae growth. Black or dark liners are better pond liners, as white liners reflect the heat back into the pond.


Established ponds
Where blanket weed and algae are already a problem in an established pond consider the following:

Blanketweed and other floating algae should not be removed by pulling them out, unless really prolific, because the spores produced by the weed will be returned to the pond causing more weed to grow.

Pond algae can sometimes be discouraged by floating a mesh bag of barley straw on the pond. About 50g of straw per square metre of water surface area is ideal.

Add the straw in spring and remove it once it has turned black (usually six months later). Lavender may be added to the straw for additional effectiveness.

For smaller ponds and water features try a liquid barley straw extract, other products may include barley straw extract with a blend of micro organisms designed to remove nutrients from the water and reduce algae growth.

Vegetation filters - A diversely planted pond is very important for water clarity. Any fast growing plant with a good root structure for good nutrient absorption i.e. of new nitrates and ammonia with the majority of its leaves above water are good candidates to start with, such as Iris.
There are other excellent plants such a sweet flag, bulrush, parrots father and lilies.

Don't change your pond water as it will only bring short-term relief and subsequently more problems.

UV sterilisation
This usually helps with algae control, disease prevention and the redox. The time it takes to clear a garden pond with a UV clarifier can vary greatly from days to weeks, however the conditions that are causing algae growth in the first place should be improved.
 


How much UV do you need for your pond?

Purely for green water eradication, 8 to 10w per 1000 gallons is usually recommended, however chlorates and stocking levels should also be considered.

Pond dyes - these work by blocking some wavelengths of light, so the algae cannot grow. The die gradually degenerates with time, therefore has to be replaced to remain effective. Although non-toxic to animals, it will kill submerged plants.

Prevention
Aim to reduce the amount of nutrients entering the pond by the following:

only introduce plants to the water which are growing in low nutrient aquatic compost.
Avoid putting soil into the pond and remove any soil that has collected on the base of a new pond before filling with water.
Apply any fertilisers to lawns carefully to avoid waste running into the pond.
Place a pond net over ponds to prevent leaves falling in.
Use rainwater to top up levels if possible.

Other options - prevent stagnant water by having a fountain or water feature which will help aerate the water and prevent the build up of blue/green algae.

Fish and pond snails
Algae is more of a problem in a pond which contains fish, the best pond fish are Goldfish, Orfe, Shubunkin, Carp & Tench.
Feed in mud and debris at the bottom of pools can cause clouding of the water. Add fish about three weeks after filling and planting a new pond.

Keep fish pollution in check
Ramshorn snails can be introduced, but avoid other water snails as they tend to be less efficient scavengers.

Planting your garden pond
It is important in any pond or water garden to have a good balance of plants that offer a variety of foliage and colour at different times of the year for your enjoyment. Plants are required for a successful ecosystem on any pond. This is very important, choose plant species to suit the size of your pond such as more vigorous plants for larger ponds and slower growing cultivars for smaller ponds.

Always take account of the plants final mature height, as certain grasses and rushes can grow very tall and obscure a pond. Always use aquatic compost to avoid pollution.

Oxygenating plants are essential for keeping the pond healthy. As a rule of thumb, for a well-established pond, and for a plant leaf cover of about 50% of the pond surface area. Water lilies are best for this extra shade, this cover benefits both fish and clear water in the pond since algae growth is reduced.

Guide to the number of plants per square metre in a pond
A rough guide to the number of plants you may require to start a successful pond by simply working on the approximate surface area of your pond e.g. 4 m x 3 m equals 12 m².
 

Plants

Pond surface area in square metres

 

2 m²

4 m²

6 m²

8 m²

10 m²

12 m²

Waterlilies

1

2

3

3

4

5

Deep marginals

1

2

2

5

6

8

Marginals

8

14

18

24

30

36

Oxygenating

15

30

45

60

75

90

Floating

2

3

4

6

8

12



Planting your pond plants
To get the best results, each pond plant should be planted in the most appropriate position for that cultivar.
 
 
Bog plants zone 1

Pond-side plants grow at the edge of the pond in damp or even swampy conditions, preferring a couple of inches of water covering them. Plant them directly into the boggy wet soil e.g. Marsh Marigold, Arrowheads, Goats Beard. It is important not to allow these plans to die out.

Marginal plants zones 2 & 3

These do best in shallow water at the edge of a pond, plant in containers and baskets in aquatic compost. Place onto the marginal shelves around the pond edges e.g. Iris and Water Mint.

Oxygenators zones 4 & 5

These plans are essential for keeping the pond healthy, some have roots, but most simply float in the water absorbing carbon dioxide and releasing oxygen as they grow e.g. Waterlilies, Water Hawthorne and Floating Heart.

Seasonal pond care
Spring
At the beginning of the season there are things to do, it is the time for water cleaning and plant care. Optimal water conditions can be easily achieved with basic care products. Use a bacterial supplement to kickstart the bio-filter. An algae net will remove bothersome pond growth, and to reduce subsequent algae growth, suck up the silt on the pond floor, ideally with a pond vac and you're ready for summer.

Summer
Only intervene in a support capacity, in order to maintain the beauty of your pond for as long as possible and to prevent the body of water from spoiling.
Remove undesired leaves and string algae, cutback excess plant growth, so water quality is not in impaired due to excess nutrients from the roots.
In the summer, a surface skimmer ensures a good view of your fish, also improving water quality. Make the water level is topped up, especially during dry spells when evaporation is high. Run the filter system and water courses 24 hours per day to oxygenate the pond.

Autumn
This is a busy time preparing the pond for winter. Remove silt and sediment with a pond vac, remove plant remains, cover the pond with the pond net to prevent unwanted leaves in the pond sinking to the bottom and reducing water quality. Strengthen the fish with feeding for winter.

Winter
Naturally, winter is the quietest time of year. It is important to keep at least a small section of your pond open for gaseous exchanges (oxygen and carbon dioxide). If water can still flow into the pond through a water course/fall or aeration device, that will work. Ice preventers are useful addition to prevent freezing. A minimum pond depth of 75 cm allows fish and invertebrates to hibernate. Remove leaves and cover the pond with a net as rotting leaves produce ammonia, carbon dioxide and nitric acid, thus lowering PH and KH to dangerously low levels. Decay can also lead to hydrogen sulphide from anaerobic breakdown.
Make the filter system winter proof in accordance with recommendations. Now your pond and inhabitants are prepared for the cold season.

Ecosystems
When you bring the water and plants into your garden you create an ecosystem. With care this ecosystem can both thrive and inspire. Knowing you are helping the environment will justly reward all of your effort.

Examples of living things you will find in an average garden pond:
Common frogs in 8/10 ponds.
Dragonflies, seen in 25 to 50% of all garden ponds.
Mayflies, Pond Olive most widespread.
Greater water boatmen, 30% of all ponds.
Caddis flies, found in 10% of garden ponds, a good sign of a high-quality pond.

As well as pond residents, the pond will attract a diverse range of birds and mammals creating your very own wildlife haven.

Pond predator control
Heron decoys work well and also scare other predatory birds such as owls etc.

Motion sensor scarecrows connected to a water supply will squirt at any movement around the pond.

Underwater fish decoys, can give the real fish time to escape.

Drainage pipes placed in the water make a good place to escape and hide.

Pond equipment advice
Calculating head height
 


Maximum pump head measures the vertical distance from the surface of the pond water to the point at which the water enters the water course.

Maximum head height refers to the maximum pumping height of the pump.
The stated head height of a pump is the minimum height at which there is zero flow. A pump with a 3 m head will have zero flow at 3 m.
It is important to know the height of your intended water feature. If you need 2000 L of water to run your water feature, then you must ensure the pump that you select can prompt 2000 L of water at the height of the feature.
Head height can be misleading, many by the wrong size pump, so it's important to know how much water the pump can handle at different practical heads or height differences. Pump flow rates for varying head heights are provided on this website for reference.

Total dynamic head

Other information required to calculate the total dynamic head (TDH) includes the length and diameter of the pipe leading from the pump to the outlet at the top of the water course. Working out  friction losses due to varying hose sizes and types and the number of joints is very complex.
For most garden ponds allow 10 cm of lift for every 1 m of hose length e.g. every 5 m of tubing adds 50 cm to your head height calculations. Any elbow or T-pipe will substantially reduce the flow. (25% of height for each 90° elbow), so where possible, use flexible tubing to curve around corners.

Tubing/flow rates

The hose size running from the pump is determined by the maximum flow rate of the pump selected. When selecting hoses, select the diameter that is as large as possible to avoid excessive friction losses.

How to measure flow rate
This is helpful to see if an old pump is still working effectively as it may need cleaning or replacing.
Take a container of a known volume e.g. a 5 gallon bucket, and time how long it takes to fill it in seconds at the flow you have, then divide by 3600 the number of seconds it takes to fill the container. Then multiply by the volume (gallons of the container), the result equals the flow rate in gallons per hour.

e.g. If it takes 10 seconds to fill a 5 gallon bucket;

3600/10 seconds x 5 gallons = 1,800 GPH
(For metric conversion GPH x 4.54 = LPH)

You can use this formula to find how much will you would like over the garden waterfall, by placing a garden hose at the top of the waterfall and adjusting the volume of water until you find the flow that you want.
Measure this flow to give you an idea of the volume required to get the effect you desire, for strong flows multiple hoses will be required.

Using all of these calculations you should be able to determine any requirements for pumps and filters.

What size pump do I need?
The pump is one of the most important equipment purchases you will make.
Use flow rate and had pressure to select your water pump.
You must know:

The volume of water that you will move through your system i.e. volume of the pond or water feature and filters combined.
How many times per hour you need to calculate the volume of your pond. Typically 1 to 2 times the volume per hour depending on fish stocking densities.
How much resistance (head) the pump encounters as it moves water from the pond surface to the point where the water enters the water course.

There are three main types of pond pumps according to their use:

Filter
Fountain
Water course
 


Filter pump selection
In order to select the optimal filter size, first upon volume must be calculated.

Rectangular/square ponds

Length M (A) x Width M (B) x Average depth M (C) x 1000 = approximate volume in litres.

Circular ponds

1/2 A x 1/2 A 3014 x Av Depth x 1000 = volume in litres

NOTE: Taking the average depth may involve 10 different measurements to give an average pond depth.

Once your calculations have been made, always select the pump with slightly more capacity than you require. NOTE: the filtration system needs to circulate the total effective pond volume every 1 to 2 hours.

Matching your pump to your filtration system
If you have chosen to keep your pond clean with a biological filter (pressure of gravity filter) then you must size your pump appropriately for the filtration system. If you don't have enough flow through your filter, it will not circulate the pond water often enough and therefore your filter will not clean your pond correctly. However, too much flow through your filter will result in water passing through the filter too quickly, often bypassing the filter material and giving the UV clarifier no chance to kill algae, this rapid flow can result in a cloudy pond and can cause filter damage.

In many situations separate pumps should be used for the filtration system and water feature, since bio-filters need to run 24/7 (to maintain oxygen levels and healthy filter bacteria). Other features such as waterfalls and water features do not need to run all the time.

Improve the performance and longevity of your pump
Do not shorten electrical cable as it will invalidate the manufacturers warranty.
Position the pump off the pond floor and away from silt.
Regularly cleaned the impeller i.e. every six months.
Do not restrict the flow of water from your pump - select appropriately sized hose for the size of pump.
Do not run the pump dry.
Regularly clean the pre-filter
Do not bury transformers in the ground.

Watercourse pump size calculation
As a rule of thumb for determining the right pump for water course use the following:

Width of watercourse in centimetres times 1.5 litres/min equals capacity in litres/min.

This watercourse pump can either be a pond filter pump or upon the fountain pump depending on the size of the watercourse and the degree of cleaning required. Ideally use of pond filter pump as they have the highest flow rates and require less cleaning.

Fountain/waterfall pump
(i.e. combined general-purpose pumps)

All round garden pumps which are designed to operate fountains, waterfalls and even filters simultaneously. They are usually supplied with a variety of Fountain jets and most have a foamless pre-filter for reduced maintenance.

This pump is perfect for most small to medium-sized ponds. The height and spray pattern (i.e. droplet size) is important, as finer droplets will absorb more oxygen and a higher spray will also absorb more oxygen. Foam jets are the most effective at this, however, they require more power to run (in general the more powerful pump motor, the more oxygen dioxide the spray can absorb).

The pre-filter in these pumps prevents the small holes in the fountainhead blocking with debris.
Always choose a fountain pump that comes complete with various fountainheads as well as a valve which allows water to flow to a bio-filter.

Maximum Fountain height
Minimum distance to the nearest edge of the pond. If the fountain is too high, water will be lost from the pond with splash and even worse in windy conditions.

Feature pumps
A small pump designed to operate in small self-contained water features. They are not really suitable for use in a garden pond due to the size of pre-filter, most models will have a flow control to reduce flow rate by approximately 25% plus a range of selected Fountain attachments.

Filter/watercourse pumps
These are designed to allow larger soft solids to pass through the pump so that the waste is delivered to the filter, where it is trapped. Also ideal for watercourses as they rarely block or need maintaining. Due to the pump design they are not suitable for running fountains. Often two pumps are beneficial, one of these to run the bio-filters 24 hours a day and a fountain pump to operate the fountain which can be switched off at certain times.

Solar powered pumps
Powered by a solar panel they are usually small feature/fountain pumps.

All in one pumps
This type of pump combines a biological filter and ultraviolet clarifier in an integrated unit, suitable for small ponds with low stocking levels of fish.

Pump selection and installation tips
Decide on your requirements before choosing a pump.

Always select the pump with extra capacity i.e. never purchased a pump which is just powerful enough.

If only running of filter, select a solid handling pump.

Always use the recommended hose size for the pump. Use the largest diameter holes on multistage pose tales when possible, always cut off horsetails to the correct size.

Always use an RCD trip switch

Always use a qualified electrician for the installation of electrical equipment.

Position the pump to maximise circulation off the pond floor, on a stone, away from silt.

For small or large ponds the unit is housed outside of the pond, usually by the top of a waterfall. A surface or submersible pump is used to push water through the filter medium.

Which biological filter?

Low Fish Stock
For ponds which have mainly plants and no (or few) fish and normal levels of sunlight.

High Fish Stock
For ponds with less plants and a higher stocking level of fish or exposed to high levels of sunlight.

Different types of filter
Most are available with combined UV clarifier.

Complete pond filter systems (all in one filters).
These are basic filters which are positioned in the pond, usually used only in small ponds that are lightly stocked with fish, these incorporate a pump, filter and UV clarifier in one easy to install unit. The drawback with this type of filter is that water circulation tends to be more uneven.

Pressure filters
Ideal for small to medium sized ponds they are directly fed from a pump in the pond. Since the filter is a sealed unit, the water leaving this unit is still under pressure, allowing more flexibility in positioning of the unit. Due to their small size, choose the one with a cleaning mechanism to reduce the opening up and maintaining of the filter.

Flow through filters
These filters are pump fed and gravity return, they require a pump in the pond to feed the filter. Water will pass through the filter and return to the pond through gravity. The filter outlet must be higher than the point at which you want the water to return.

Therefore it is important to consider installation options before selecting such a filter.

Gravity fed filters
These are usually only used it the pond has been specially constructed with a sloping base and bottom drains. The filter must be sunk into the ground so the water level in the filter is the same as the pond. Water enters the filter by gravity from the pond’s bottom drain and is returned by the pump under pressure. This type of filter can be used to power a Fountain Jet, or waterfall if required.



Therefore

The choice of your pond filter should be based on the size of the pond, the number and type of fish, and the area available for installation of the filter.

Pond size
Work out the volume of water in your pond.

Multiply the average length x average width x average depth

Multiply this figure by 1000 to get the volume in litres

When calculating pond dimensions in feet, convert this measurement to gallons by multiplying by 6.23

Which UVC filter?
You will need to know your pond volume to choose a suitable UVC.

To find the correct UVC for your pond, also consider the stocking and sunlight levels. If either of these are high, always pick the UVC based on the high fish/sunlight level rating.

Calculate the right UV clarifier power

Pond without fish stock 1 WUVC power per meter cubed of pond volume.

Pond with fish stock 2 WUVC power per meter cubed of pond volume.

Pond with koi stock 3 WUVC power per meter cubed of pond volume.

UVC bulbs should be changed in spring to guarantee full strength capacity of UVC lightwaves.

Installing a biological filter
Gravity return biological filters have a gravity outlet. The outlet must be higher than the point of return.
To maximise water flow, and ensure the largest possible inlet is used.
Gravity outlet filters, keep the return pipe full bore, gently sloping down and as short as possible.
Most top outlet filters work better if partially buried, keeping the sides tight around the media when full of water.

Running a biological filter
Filters must be run 24 hours a day (certainly from March to October).
Pass your pond water volume through the filter at least every 1 to 2 hours.
Regularly check pump pre-filter to ensure a good flow.
Remember a filter can take up to 6 weeks to fully biologically activate.
Clear water does not mean healthy water, test your water regularly.
Use a bacterial supplement to kickstart and improve filter performance. At this point have UVC off to avoid any ? effect.
Always clean filter material in a bucket of pond water and not in tap water.
Only clean media when flow is being restricted.

Pond Aeration
Barometric pressure, altitude, salinity, water purity and biological oxygen demand or affect the amount of naturally occurring dissolved oxygen levels in water. The amount of additional oxygen water can hold through the aeration process is a function of temperature, altitude, and salinity. Colder water holds more oxygen than warm, water in higher elevations or with higher salinity levels has a decreased saturation level of oxygen. Once you have reached the saturation level, oxygen cannot be added without the help of photosynthetic activity or the introduction of pure oxygen.

In ponds, the introduction of oxygen via some type of aeration device can:

    Allow for greater densities of fish

    Speed up the rate of organic decomposition

    Improve overall water quality

    Reduce the amount of phosphorus, which would otherwise be available for plant growth

    Decrease the severity of algae blooms.

 
Note: There are a number of types of aeration devices available in our pond aeration section.
 

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