The scourge of green water – a bloom of single-celled algae suspended in the water – is one of the most common problems to plague pond-keepers especially in spring and early summer. Though it was once a major bane of fish ponds and water gardens, fortunately today, with the advent of affordable ultra violet (UV) clarifiers, it is one of the easiest things to cure. Easy to install and cheap to run, UV clarifiers make these microscopic algae, which on their own are too small to be removed by normal filtration, clump together to form larger particles which the filter is then able to trap.
Selecting the Right Clarifier
A quick look at the units available will reveal a wide range of sizes, types and designs by most of the major pond equipment manufacturers, including Hozlock, Interpet, Lotus and TMC. There are clarifiers available rated from 4–55 watts suitable for the smallest of ponds right up to 10,000 gallons – and ponds which are larger than this can use multiple UV units to achieve the necessary level of clarification. With a relatively modest price to buy in the first place – from around £50 to £200 – and running costs for even the largest commercially available units amounting to a little less than the equivalent of a domestic light bulb, clear water has never been a more affordable prospect.
Picking the right one for your pond depends on a number of factors – and top of the list is the volume of water it contains, with stocking levels, planting density and amount of shade also being key considerations. It is impossible to have too big a clarifier for your pond – but far too easy to be under-equipped – so to make sure of the job, it is always better to err on the side of a model with slightly larger capacity than is perhaps absolutely necessary.
It is important to consider the capacity of the bio-filter also – since the addition of UV clarification will increase the load placed on this part of the set-up by contributing a significant number of clumps of dead algae which then need to be removed from the water. If the filtration unit is also new, or has recently been cleaned, it is often best to run the filter for three weeks to a month before switching on the UV, to allow the necessary resident colony of bacteria to grow large enough to cope with the additional strain. Most manufacturers also produce combined bio-filter/clarifiers, which are ideal for some ponds.
Installation and Maintenance
Most UV clarifiers are located between the pump and the filter and, since the unit will need occasional cleaning and the bulb will need to be replaced yearly to guarantee full efficiency, the unit needs to be positioned somewhere which makes it accessible for maintenance. It is also a good idea to put the UV unit on the same circuit as the pump – so that if the pump stops working, so does the clarifier, avoiding any potentially harmful build up of solids on the surface of the bulb’s protective tube.
These units need surprisingly little in the way of maintenance, apart from the occasional cleaning of the delicate quartz tube which surrounds the bulb and the yearly replacement of the ultra violet bulb itself. If the clarifier is not being used in the winter – and there is seldom any need in the UK to run one year-round – it should be drained, cleaned and stored carefully ahead of being brought back into service in the following spring.
While these units are superb at removing the algae which cause green water, there is a danger that with this particular algal trouble gone; blanket weed is left with an open opportunity to thrive, which may call for additional treatment, particularly in the early part of the year. However, this need not be a major problem. A wide range of pond treatments are available to deal with this problem and for those who prefer to stay more high-tech a variety of easily installed electronic systems are also on sale to keep blanket weed under control. Water Habitats, for example, offer a device which generates ultrasonic waves to break up algal cells, while Blagdon supply a unit which sends an electrical pulse through the water to disrupt calcium ions and bring about the same effect.
Ultra violet clarifiers represent a decidedly modern and affordable approach to maintaining clear water, being simple to install, easy to use and very cheap to run. With their many virtues, small wonder that any pond seems incomplete without one.
Last Modified: January 25, 2022
We’re not sure what set-up you have but are you sure there is no leak?
We have just moved into a new house and inherited a pond with 8 koi carp. It has a “pond clear advantage UV15 ” filter unit .. the waterfall seemed to work fine but then the levels keep dropping in the tanks with the filter? Any ideas please would be very helpful