What is green water? This is a common question faced by many fish pond keepers. So here is what you need to know about what green water is, how it occurs and what you can do to achieve a crystal clear pond.
What is green water?
Green water is a form of algae that has grown and thrived in your pond. Green water needs only light, water and nutrients in order to survive. The more of these ingredients that are made available to the microscopic algae, in the form of sunlight, biological matter and of course pond water, the faster the algae will grow. Not only does this have an unsightly effect on the pond, but it can also lead to serious health problems for the fish.
The important thing to remember if you should find that your pond does have green water is that this is a very common problem and is easily treatable.
What causes green water?
Green water occurs for a number of reasons. However the most common cause is that there is an over-abundance of either sunlight or nutrients in the pond. Nutrients can count as anything on which the algae can feed and spread, such as by over-feeding fish food, and even the waste of the fish themselves. The most common of these nutrients include phosphate, nitrate, nitrite and ammonia.
Above: Green water in the wild.
Green water is especially common during the summer in which the algae is receiving large amount of light. This will rapidly speed up the growth of the algae and presents the risk of starving the pond of oxygen.
Will draining the pond and replacing with clean tap water eradicate the green water?
This is a common misconception by pond keepers, hoping that by flushing away the water you are getting rid of the green water, but this is in fact making the problem worse because of the nutrients present in the water. Other than actually seeing the green water in the pond, another way to confirm its presence is to using a pond testing kit to test for high levels of nitrate and phosphate. These are the two main causes of green water.
Every time the pond is topped up with fresh tap water, the nutrient rich water is actually feeding the green water algae. The key to defeating green water is by either starving the green water of the nutrients and light it requires to thrive, infusing the pond water with chemical treatments, or by exposing the pond water to ultra-violet rays.
Does green water hurt my fish?
Green water does present other health risks to pond fish if it is allowed to grow. By dramatically effecting the levels of oxygen within the water it is literally starving the fish of oxygen, which is especially dangerous for ponds which keep larger fish, as they require larger amounts of oxygen.
As the green water within the pond starts to grow it begins to require more oxygen in order to survive. It obtains this oxygen by extracting it from the water in which the fish live, which can result in a condition known as ‘summer fish kill’.
This condition is when the pond water has become so devoid of oxygen that it can no longer support the requirements of the fish, meaning that they begin to die. It is most common in mid-summer, as this is when the green water is receiving the highest levels of light and heat. Since warm water contains less oxygen it is vital to aerate the water at night. This will provide the fish with suitable levels of oxygen.
Green water will also prevent sun rays from penetrating the surface of the water, which further compounds the problem by reducing growth rate of oxygen producing pond plants.
What is the best pond green water treatment?
As green water is such a common problem there are a number of green water treatments that have been developed to help combat it. One of the most natural ways to fight green water is also the most basic. By introducing plant life to the pond you are actively depriving the green water of the nutrients present in the water, which is requires in order to thrive. Pond plants also shade the algae, thereby cutting off the amount of sunlight being provided to the green water.
Above: Swell own Brand 'Control Green Water'.
To thoroughly eradicate and prevent green water in a pond, the most reliable treatment is to install a UV clarifier. UV clarifiers usually come as part of a filtration system, such as with the Blagdon Midipond Pond Filter. As the pond water is exposed to the UV clarifier, the algae cells will be killed and thus be unable to propagate.
Other methods of treating the pond water include the use of barley straw, the removal of nutrients from the pond, or through a chemical algaecide.
How can I prevent green water happening again?
The most reliable way to prevent green water in your pond is to ensure that your pond’s filtration system comes with a UV clarifier. If the clarifier is functioning properly, is well maintained and is designed to meet the needs of your individual pond, it is widely considered the easiest method of keeping green water at bay.
Flocculants are another way of preventing green water occurring again. These water treatments work by causing the green water algae to clump together, which makes them big enough to be easily filtered out by the pond filtration system.
Does barley straw stop green water?
Other methods of controlling green water include introducing barley straw to the pond. This can be bought from Swell UK in regular bales, such as the Bermuda Barley Straw Bales and is a useful way of controlling certain types of pond algae. It also has the advantage of being cheaper than other methods, however the algae disrupting chemicals released by the barley during decomposition are a relatively short-term solution compared with UV clarifiers.
The great advantages of using barley straw to prevent green water are that it is so readily available, easy to use and also environmentally friendly. As the barley straw starts to decompose it releases algae disrupting chemicals, which help to prevent the algae from thriving.
Why is my UV clarifier not working on green water?
Green water can still appear in ponds that have a UV clarifier as part of the filtration system, especially when pond keepers construct their own filtration systems. The reason that this is often a problem is that the pond water must be allowed sufficient contact time with the UV radiation in order to be effective. If the speed of the water pump is too high it is not allowing the water enough exposure to the UV, greatly reducing the effect.
Another reason that a UV clarifier may not be coping is because a number of fish in the pond is too high. As the fish produce waste, more nutrients are being added to the pond, which in turn encourages green water. In this case the best thing to do is either add an additional UV clarifier to the filtration system, or to purchase a larger filtration system which can cope with the amount of waste being produced.
Above: Blagon in-line UV Clarifier.
It is also important to regularly replace the UV bulb as the quartz sleeve which houses the bulb can become dirty or damaged. There is also the possibility that the bulb has simply lost its potency with use. In order to provide maximum UV levels it should be replaced approximately every six months.
By Sam Bainbridge