UV pond sterilisers are a great way to remove harmful bacteria and pathogens within the water.  These require a UV bulb to operate as this is done by using ultraviolet light.  UV light draws together single celled algae (a well known cause of pond water looking green) and neutralises the harmful bacteria and pathogens to give you a cleaner and healthier pond.  

Identifying Your Specific Bulb Requirement

The first step is to check the documentation and advice given by your UV steriliser model.  The manufacturers of these sterilisers will often design their units to work with a particular type of bulb.  Choosing may mean it does not fit or is not compatible once fitted leading to the UV steriliser not working as it should which could do potential damage to the bulb and the steriliser itself.  

• Diameter: The majority of UV sterilisers will use T5 or T8 low-pressure quartz glass lamps.  The “T” number given on these tubes refers to its diameter.
• Wattage: The power rating (such as 9w or 18w) must match the steriliser’s requirements. The wattage determines the amount of UV output emitted and is related to the amount of water the unit can cover in treatment.
• Length and Base Type: The bulb must be the correct physical length to fit securely inside the unit. They will usually have a two-pin or four-pin base connector referred to as G5 or G13.  If this information is not on the lamp within the unit it should be covered in the included documentation for your steriliser.

When looking for a replacement bulb for your sterilisation unit  always look for the terms Germicidal or UVC.

Which Type UV Rays Are Used in UV Water Purifiers?

UV water purifiers, including those used for ponds use a type of radiation called UV-C radiation.

Ultraviolet light comes in three different types:

• UV-A: This has a wavelength range of 315-400nm and is used for tanning and blacklights.  These are not classed as germicidal.
• UV-B: This has a wavelength range of 280-315nm and is used for medical reasons in some skin treatments.  It has limited germicidal use.
• UV-C:  This has a wavelength range of 100-280nm and is used for germicidal purposes and can disrupt DNA meaning it cannot be used anywhere where any one may be looking at the light.

The most effective wavelength for germicidal light occurs around 254 nanometers (nm). Standard low-pressure mercury lamps have been found to be the most efficient at producing UV light at this wavelength. This UV-C light is great for targeting algae, bacteria, viruses, and protozoa in water by preventing them from reproducing.

What Are the Different Types of UV Lamps?

There are three options available for the different type of UV lamp that can be used for water treatment:

1. Low-Pressure (LP) Lamps:  These are the most common type used in residential and smaller commercial and pond systems. They are similar to standard fluorescent tubes but emit a UV-C light instead.  They have a highly efficient wavelength that produces a monochromatic light peaking at 254nm.  They often have a long advised lifetime of 9000 - 12000 hours and generally have a lower cost.
2. Medium-Pressure (MP) Lamps:  These lamps are designed to operate at higher temperatures and pressures.  They are normally used for larger scaler or industrial levels of water treatment.  They produce a broader polychromatic spectrum of UV light ranging from 200-300nm.  As they have a higher power output they can treat larger volumes of water at a faster rate and have a lifespan of around 4000-6000 hours.
3. UV Light-Emitting Diodes (UV-C LEDs):  This is a newer type of UV-C technology beginning to emerge using solid state components.  They can be engineered to emit the desired wavelength.  They will use a lower wattage and are mercury free making them a more environmentally friendly choice.   

If you are looking for a UV bulb for a pond purifier, you should focus on UV-C bulbs which primarily emit at 254 nm, this being the germicidal wavelength necessary to combat green water algae and other harmful pathogens.