Understanding Algae Problems in Your Pond
Green water can be a problem in both new and mature ponds. So what is it?
Green water is caused by very small algae which are suspended in your pond. They grow at an alarming rate (upto thirty times an hour in perfect conditions) feeding on nitrates and phosphates.
Persistently green pond water is extremely disheartening. The pond looks uncared for, you cannot see your fish and those that you can see may seem lethargic due to lowered oxygen levels. Both new and mature ponds will experience green water problems when the level of nitrates in the pond increase or there is an excess of sunlight. As the pond heats up during the day you may find also that algae “blooms” rise from the bottom of the pond, sinking again as the sun goes in and it becomes cooler. The green algae exclude light and absorb oxygen from the water and can lead to rapid changes in the pH of the water and a reduction in oxygen levels. Both of these cause stress in fish.
So what is to be done?
To find a solution it is necessary to understand just what is happening in your pond. Fish produce ammonia and waste matter and are in effect swimming in there own effluent. Fortunately, there are naturally occurring bacteria which are found in ponds that convert ammonia into nitrite and subsequently into nitrate. In addition, air bourn matter is carried into your pond and plants die back and decompose at the bottom of the pond. The bacteria slowly convert the “sludge” into nitrates. You now have a perfect environment for green algae to thrive.
Overstocking with fish, especially koi carp, may be one of the causes. Your filtration system may be large enough for the density of fish in your pond and green algae is a sign that the filter is doing its job. The filter is designed to grow copious amounts of bacteria, thereby generating copious amounts of nitrate… which algae love!
The most effective solution is to fit an ultra violet unit. However, other treatments are available and these are covered later.
Ultra Violet Light Clarification (UVC)
Ultra Violet Light is deadly to algae and the UVC unit is usually placed between the pond pump and the filter (pump fed filter system). Water is pumped from the pond and through the UVC. Any algae spores in the water will be destroyed and the dead algae are collected in the filter. A filter will not collect live algae as they are small enough to pass through filter foam. Dead algae forms into clumps, known as “flocs”, which can be collected in the filter medium.
A UVC will not kill blanket weed, nor will it kill bacteria or viruses. A special type of sterilisation UVC would be required. Fortunately the light from a UVC will not harm plants, fish or filter bacteria. As a word of caution – NEVER EXPOSE YOUR EYES TO UV LIGHT. This is very important!
Choosing a UVC unit
UVC units will provide clear water when installed correctly and the size of the unit (measured in WATTS) is sufficient for the size of pond, type of fish and fish stock density.
The UVC lamp must be replaced annually. We recommend doing this at the beginning of April, thereby ensuring the unit is running at maximum capacity as the algae start to bloom. The lamp will start to deteriorate after six months but from October onwards the water is cooler and the level of algae in the water drops.
It is important that the UVC unit has a quartz tube/sleeve incorporated into the unit. This insulates the lamp from the water allowing the lamp to reach its optimum operating temperature of 40 degrees C. Dead algae can adhere to the quartz tube and it should be cleaned at least annually, otherwise performance will fall. If you have a very green pond and it does not start to clear in a week then check the quartz sleeve. (note : the quartz sleeve is strong but brittle. Make sure that you do not snag it on the UVC unit when removing as it will crack and will need to be replaced.).
Manufacturers make varying claims for the performance of their units. As a very general guide 10 watts of UV power will be about right for a 1000 gallon (4,500 litre) average fish pond. If the pond is in full sun light or the water is shallow or you are in any doubt go for a larger model – you cannot overdose. We recommend that the unit is run 24 hours a day. The running costs are relatively low … and algae does not switch off at night or the weekends.
We strongly believe that this is the best solution for green algae. If you buy one you really will not regret it. We have found that Kockney Koi’s Yamitsu and T.M.C.’s units are very reliable and easy to maintain.
Natural Remedies for Green Algae
There are a number of products available (see Pond Treatment /Green water Treatment section).
Nishikoi’s Goodbye Green Water is a favourite with our customers. It comes as an 8 sachets pack. One sachet per 1000 gallons has to be placed into the pond or filter every week.
Bio Claire is an excellent natural product and is an effective preventative in that it generates bacteria that break down fish waste and sludge on the bottom of the pond. Instead of turning the sludge into nitrate the bacteria generate nitrogen gas which permeates through the water. This deprives the green algae of nutrients. It is slow working but effective and monthly maintenance doses are required.
Barley Straw Extract and Organic Barley Straw. It was found that by placing large bales of organic barley straw into lakes that blanket weed and green (and blue) algae problems were much reduced. The chemical process introduces low levels of hydrogen peroxide (2ppm), this interferes with the algae photosynthesis process and is very complex. Also, as a natural product, it is almost impossible to over dose the pond.
There are a number of safe to use chemical algaecides. However, we recommend that natural products are used initially, only using chemical products if problems continue. When using chemical treatments, as with fish medication treatments, care must be taken not to overdose, to ensure that ammonia and nitrite readings are zero and that that the pond is well aireated during treatment.
