The only reason a pond would ever turn green is due to algae growing in it. First, let it be said that algae in a pond is not necessarily bad. In fact, a healthy thin layer of algae growing on the inner surfaces of the pond is an important part of a healthy pond. It can help prevent a high level of nitrates from building up in the pond water by consuming the nitrates as food and giving off oxygen in the process. On the other hand, algae can also be a real problem.
In the ﬁrst situation, your pond water, which was once clear, has suddenly turned green. Here is what has happened. The “good or healthy” type algae which usually collects on the sides of the pond and never grows to be more than 1/4″ in length has decided to reproduce or bloom. Similar to how a ﬂower might bloom and give off pollen, this type of algae will suddenly release millions of single cell algae, only 3 microns in size. These cells, while they are alive, are too small for any ﬁlter to pick up.
How do you control algae blooms? The easiest and often times, most practical way to solve this problem is to simply install an ultraviolet light on your pond’s ﬁltration system. The way an ultraviolet light works is simple. As the water from the pond ﬂows through the ultraviolet light unit it gets exposed to the light waves emitted from the light inside the unit. These light waves are so intense that they break up the DNA in the algae’s cell thereby killing the algae. Once the algae dies the dead cells start to decompose and then begin sticking to one another. After a number of the dead algae cells collect together, their total mass then becomes large enough for the ﬁlter to collect them out of the water or they simply sink to the pond bottom. Once you install an ultraviolet light this process takes about a week before the water becomes clear again.
In the second situation, your pond water may be clear but a green stringy algae reaching 1 to 2 feet long is rapidly beginning to grow on the waterfall and or throughout the pond. This algae may start to become a problem as it breaks loose and begins ﬂoating around in the pond. Additionally, as this algae ﬁlls the basket, the basket may need to be cleaned almost daily or the will slow down or completely stop ing water. In this case, the problem is that you have developed ﬁlamentous algae in your pond. This algae is most commonly introduced to a pond when you add plants. If a single spore is on a plant when you place it in your pond you can create this problem.
This “string algae” as it is often referred to comes in many forms. Some grow very quick and are invasive while others grow very slowly. Some forms may not be very obvious at ﬁrst glance but will grow to about 2 to 3 inches long on the pond walls. With this form of algae you notice the basket walls quickly gets lined with green algae to the point that it affects the water ﬂow of the but the basket itself has very little debris in it. It is impossible for the “good” algae mentioned in the ﬁrst situation to plug a basket due to it’s small particle size.
How do you control ﬁlamentous algae? An ultraviolet light will have very little affect on ﬁlamentous algae because this type of algae grows on the pond walls and never reaches the uv light. In mild cases you can simply collect the algae off the waterfall or rocks by hand when it becomes unattractive. In severe cases when it becomes very invasive and starts plugging the basket, we recommend using an algae control liquid. We have a product called Algae Control which has worked very well for us. It is a herbicide which means it is a weed killer. When dosed properly it is extremely effective but you need to know how many gallons you have in your pond to properly use it. If you overdose by as little as 20% you can kill your ﬁsh. We suggest you under dose the ﬁrst couple times you use it if you are not sure of the volume of your pond. One or two normal doses will usually kill off the algae. Then, we recommend adding half the recommend dose once every two weeks, rather than once a week, as a maintenance. Always keep your running to help provide oxygen to the pond while treating with this product because as the algae dies, and begins to decompose, it can consume large amounts of oxygen from the water. You need to pay attention when you use this product but it by far the easiest and most effective product we have used to overcome ﬁlamentous algae.
Tips concerning ultraviolet lights