Pond Questions and Answers

Author: Richard Guest of Pets Parade Team

Do I need a filter on my pond?
It is perfectly possible to keep fish in your pond without a filter provided you maintain a very low stocking rate and keep smaller growing species such as gold fish, shubunkins and sarasa comets. Waste excreted by the fish will be diluted in the water and broken down by naturally occurring bacteria and by plant growth. Keeping too many fish will lead to a deterioration in water quality and will probably result in illness and death in your fish. A filter acts to break down waste products from the fish and maintains healthy water quality. Therefore if you install a filter system on your pond it will enable you to keep larger numbers of fish and also improves their environment.

How does a biological filter work?.
The fish in a pond excrete large amounts of ammonia as a by-product of their metabolism, they are in effect swimming around in their own toilet. The main function of the filter is to act as a sewage treatment plant for your fish, it does this by providing a large surface area for bacteria to colonise. These bacteria break down the Ammonia and convert it first into Nitrite and then into Nitrate, which is
relatively harmless to pond fish. The filter is in effect a living organism in its own right, hence the term biological filter. It takes five to six weeks for the necessary bacteria to become established in a new filter, during this period it is important to stock the pond gradually, adding a few fish every week. The filter must be operated 24 hours a day to supply the bacteria with a constant supply of
oxygen and food. When the filter media needs cleaning it is important to only wash with water from the pond, cleaning the filter with tap water containing chlorine will kill much of the bacterial colony.

How fast should the water in my pond be circulating through the filter system?
On ponds up to about 4000 gallons all the water in the pond should pass through the filter in a 1 to 2 hour period for best results. In larger ponds a turnover rate of every 2 - 3 hours has been found to work quite adequately. So for a pond of 1000 gallons a pump that circulates 500 gallons an hour through the filter would be fine. Remember to choose a pump that will move the correct amount of water per hour at the height and distance you need to pump it. Most pumps quote the maximum capacity they will circulate and this will drop dramatically if you need to lift the water up to a high waterfall for example.

What size pump do I need to work my waterfall?
You need to have 50 gallons of water per hour flowing for each 1" width of waterfall (27L per 2.5cm) this will give an unbroken flow across the entire width. You may increase this to achieve a faster flowing waterfall according to personal taste. A good way to judge the amount of flow that appeals to you is to run water down the fall from a hose pipe until the desired look is achieved and then measure the flow rate with a suitable container and a watch. Remember to purchase a pump that will give the required gallons/hour at the height of the top of the water fall, many pumps quote their maximum flow rate which will reduce the higher they are required to lift the water.

I have an ultraviolet clarifier fitted to my pool, and the water is crystal clear, why do I need a biological filter?
The purpose of a UV unit is to kill off green algae and provide clear water to enhance the appearance of the pond, it has no effect on improving the water quality for the fish. With a U.V fitted it is perfectly possible to have wonderfully clear water that is full of dissolved metabolic wastes such as Ammonia and Nitrite that are poisonous to the fish. An ultraviolet clarifier should be used in conjunction with a biological filter to provide water that is clean to look at, but also healthy for the fish.

I have fitted an ultraviolet light to my pond and the green water has gone but I still have blanket weed, why hasn't the ultraviolet killed this as well?
Ultraviolet lights only affect organisms that pass through their housing, they can clear up green water because they kill off the algae cells as they pass past the ultraviolet. Blanket weed remains anchored to the poolside and so is not exposed to the effects of the U.V unit.

How often should I feed my fish?
During the spring and summer months once the water temperature is over about 600F (160C) you can feed your fish 3 or 4 times a day, but make sure that you give only enough food for the fish to consume in about ten minutes. Feeding little and often is by far the best method as large amounts of uneaten food will pollute the water. As the water cools in the autumn, cut down the amount and frequency of the food and change over to a wheatgerm based food for the colder months. This is more easily digested at lower water temperatures. During the winter feed only on milder days, just once in the morning, this avoids the risk of undigested food remaining in the fishes intestines if an afternoon feed is given and then a cold night follows. Do not feed at all below 450F (60C).

How often should I change the water in my pond?
For an average garden pond changing 20% of the water once a month from March to October inclusive should help give good water conditions with minimum disturbance to your fish. Small regular water changes like this are much less stressful to the fish than large infrequent changes or an annual "spring clean". Remember to add the correct amount of water conditioner to remove chlorine from the tap water when you refill the pond.

Why do I need a test kit for my pond, I can see the water is clean?
Aquatic test kits show up levels of fish waste in the water: Ammonia, Nitrite and Nitrate, all of which are detrimental to the fish and in the case of Ammonia and Nitrite can be fatal at high levels. Because these substances are all dissolved in the water they are not visible and it is quite possible to have water that is clear and appears clean but which is extremely unhealthy for your fish.

How many plants should I keep in my pond?
The general rule of thumb is to cover approximately one third of the pond surface with plants, but you can have more or less according to personal taste.

Can I use standard garden compost for my pond plants?
No, garden compost is far too nutrient rich for a garden pond and will probably lead to an algae bloom or blanket weed, it may also contain chemicals that are toxic to fish.

Are there any conditions I should avoid for water lilies?
Water lilies do not like water splashing onto their leaves, keep them away from waterfalls or fountains.

Is it all right to turn my pump off at night?
It is best to keep the pump circulating water 24 hours a day through out the summer months. Aquatic plants will be adding oxygen to the water during the day time when they are photosynthesising, but during the night this process will stop and the plants will continue to absorb some oxygen for their own use. This leads to a drop in the levels of dissolved oxygen at night. Warmer water also holds less oxygen and the combination of turning off the pump, warm water and a planted pond causes large numbers of fish mortalities every year. There is little risk of this happening during the winter when the colder water will have a much greater oxygen content, but if you have a biological filter system then this still requires a water flow over winter.

Can I keep Koi in my pond with my other fish?
Koi will live quite happily alongside Goldfish, Orfe and Shubunkins etc, but please bear in mind the ultimate size they can reach. In view of the fact that koi can quite easily attain a length of 25" or more then it is better not to keep them in a pond of less than about a thousand gallons.

Should I keep salt in my pond all year round?
Koi and goldfish are fresh water fish and while a low level of salt may not appear to cause any problems, it is better to keep your fish In fresh water unless using salt or a specific problem such as the treatment of ulcers.

I've been advised to treat my pond once a month with anti parasite treatment as a preventative treatment, is this a good idea?
No, most medications have undesirable side effects such as reduction of oxygen level or killing some of the filter bacteria. Your fish should only be subjected to these effects if there is a specific disease problem in the pond that poses more of a risk to their health. Even then it is important to ensure the water quality is correct and to identify the cause of the problem before commencing any treatment. Poor water quality kills more fish than any disease and testing the water parameters should always be the first step if your fish are unwell.

How deep should I make my pond?
You should have a minimum depth of 18" (46cm) but a depth of 24" (61cm) will provide better protection from the extremes of weather for your fish. These recommended depths are for a pond containing smaller growing varieties such as Goldfish, Shubunkins and Sarasa comets, if you wish to keep koi it is recommended that a minimum depth of 4 feet (122cm) should be allowed.

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