With most things, prevention is always easier than the treatment and that is true to be said about green algae filled ponds. If your UV unit is managed correctly, at the right time of year, it will ensure the algae stays away and doesn’t create a pea soup pond.

Below is information on what algae is, how your uv unit controls its growth and the importance of servicing these units.

What is algae?

Algae is a term used to cover a range of simple, non-flowering and commonly aquatic plants, with many existing as single-celled forms. It can exhibit itself in several colours however commonly it appears green, which gives the water a pea-soup colouration. Algae will always exist within any body of water, although at small quantities these microscopic organisms may not be apparent, although at larger and denser quantities the clarity of the water can begin to suffer.

What makes up the algae’s food?

Food for the plants is in the form of nutrients.  Many different elements make up these nutrients, but the two we concentrate on are nitrate and phosphate.  These are both measurable by a standard pond test kit set and controlling them always reduces algae growth.

Nitrate is the last stage of the nitrogen cycle, the biological process that happens in any aquatic system (whether it be a pond or aquarium).  Nitrate is considered relatively safe to your pond in lower doses, and in a perfect world, we would carry out small water changes every month with nitrate free water, and keep the nitrate level diluted and under control.   The problem is that nowadays nitrate can often be found in high levels in tap water (one of the results of fertilisers applied to crops in fields which then get into our water system).  Depending on where you live, water changes using tap water are therefore not as effective as we would like.

Phosphate is the other nutrient which is within our control.  It comes into our ponds from four main sources, all of which we can control to some extent ; soil in planting baskets, fish food, tap water and run off.

Planting Basket Soil in your pond is a first source of phosphate, as it contains low amounts of phosphate.  The actual quantity can be quite variable, and garden compost (sometimes recommended in garden books) can have quite high quantities within it.  This phosphate will leach out of the soil over time straight into the pond water.  ACTION – Using a good quality aquatic soil, (or just gravel if the plants you are growing are low in requirements for nutrient) helps to reducing the availability of phosphate from this source.

Fish food.  Phosphorous is put into fish food as part of the diet, being an essential element for fish health.  When you feed your fish, some of the food will inevitably not get eaten and processed by the fish, and therefore it again leaches into the pond water.  ACTION – use a good quality fish food, and do not overfeed.  Feed the fish in small quantities, and make sure all the food is eaten within 3 minutes and not left floating around the pond for a long time afterwards.

Tap Water is also a major cause of phosphate.  It is another additive in fertilisers for crop production and gets into our water supply the same way as nitrate, meaning water changes also add phosphate!  ACTION – This one is a bit trickier to deal with, but with a small pond you can add rainwater to your pond rather than tap water.  Alternatively, add a phosphate absorbing filter media cannister to your hosepipe when topping up your pond, which will dramatically lower the phosphate added to your pond.

Run-off water can also be a cause of phosphate levels accumulating.  Run-off water first washes over your garden, and as it travels the phosphate leaches into the water from the surrounding soil (especially if you add fertilisers to your garden or lawn).    Note, this is only a cause where run off water can enter the pond – a raised pond, or one with a solid barrier around the edge will not suffer from this. ACTION – ensure any water from your garden is directed away from entering the pond.

What is the purpose of my UV?

A UV unit is essential to every pond in the height of our British summer, with the sun beating down onto the waters surface it provides algae with one of the most important requirements for replication. Along with with more intense sunlight and the long days there are also higher nutrient levels in the water promoting rapid growth of algae.

The purpose of a UV unit is to manage the levels of floating algae within your pond. These systems work by having water pass through the unit, which houses an ultraviolet bulb. This bulb produces a high intensity light which kills the microscopic bacteria as it passes through.

what is involved in servicing a UV unit?

A UV unit will require regular maintenance to ensure that it is running efficiently but once a year it will require a full strip down and bulb change. It is important that this is done to ensure that the UV continues to run for as long as possible.

This full strip down will include a thorough clean of the quartz sleeve which houses the bulb. Since these can become covered in silt and dirt, giving it a thorough clean allows for the light to pass through without restriction.

At this time the O-rings, which create a water tight seal between the quartz sleeve and the electrical unit, should be checked and replaced if required. As this is an essential element to stop water from getting into the electrics we always suggest replacing them since they are an inexpensive way of extending the lifespan of the Unit.

Perhaps most importantly is the installation of a new bulb. The manufacturers recommendation is that these are changed every six months, however we find that if changed in the Spring time then it only required annually. This is because the bulb is at its strongest through the Spring and Summer months, subsequently losing efficiency as Autumn and Winter roll in, with shorter days and less intense light algae will hardly grow.

If this Servicing is carried out at the right time it will leave your pond looking lovely and clear of free floating algae throughout the whole year!

The Pond Guys are a pond installation and maintenance business based in Surrey, with teams covering London and the South East.

We are specialists in all types of ponds from ‘state of the art’ Koi ponds through to tranquil water gardens and water features.

Do get in contact for any help and advice, or indeed if you need help with any aspect of your pond or feature.

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