Does the use of a UV sterilizer in an enclosed recirculating system like our ponds have other benefits besides killing off free algae? In addition, is it really a necessity?

Q:

Does the use of a UV sterilizer in an enclosed recirculating system like our ponds have other benefits besides killing off free algae? In addition, is it really a necessity?

A:

Ultraviolet light has an effective wavelength between 190 to 300 nm (1900 to 3000 Å) produces energy that kills bacteria, viruses, fungi, and small protozoans. The most effective wavelengths are in the 2500 to 2600 Angstrom range. UV light kills these organisms by interrupting the genetic chemistry (DNA) of the cell. 

 However, some of the oxidants produced by the UV light may effect the redox potential of the water, which improves the entire environment in which the aquatic animals live. UV units such as the ones used in our ponds have most of its energy wave length at 2537 Å and it does convert an infinitesimal amount of nitrate back to nitrite. Yet, the quantity of nitrite is so de minimis that it is effortlessly converted back to nitrate by the biofilter. 

Unlike ozone, there is little to no potential for destruction of any microorganisms in the system that does not pass through the UV light unit. Therefore, a UV light sterilizer is thus safer and less complex than using ozone applications. Depending on the Ultraviolet Sterilizer system, and the size and condition of the UV unit and light, the effectiveness of the unit would vary from very effective to useless. I use a UV sterilizer not to eradicate algae, but to prevent the spread of bacteria, viruses, and parasites in the ‘water-body-proper’. 

Placing the UV light at the end of a pre-filter line, just before water returns to the filtering system maximizes the sterilization process. Including killing harmful microorganisms that traveled through the mechanical and biological filters and pre-filters or any bacteria that has shed itself from a filter media during water passage. UV waves can only penetrate a maximum of about two inches of water depth and penetrating through freshwater is easier than through saltwater.  

 Make sure, that when you buy a UV unit that it has a diameter of at least three inches (a three inch diameter unit will have a 50% better kill rate than a two-inch diameter unit will). In addition, use a unit that uses one of the high output UV (GT5) style ultraviolet lamps. This is because a unit with a UV lamp that has one of the higher output lamps will give you twice the life expectancy out of the lamp, compared to a conventional germicide UV-lamp unit will. 

A big mistake people make, is running too much water flow through the UV unit. For example, a 40-watt UV light at three inches in diameter should only have water passed through it at a rate no greater than 900-gph (3406.8-lph) maximum. Most manufactures will give flow rates of 25 to 30 gallons (94.6-113.5 Liters) per hour per watt through a ponds UV unit; this should provide adequate sterilization of the systems water. This is considered a maximum flow rate, a slower flow rate, of 20-gph/watt (75.7-lph/watt) (which is the one I most recommend), will produce a better kill if UV light efficiency has declined and/or disease problems exist.  

It must be brought to your attention that the more rapidly water flows through the UV unit, the more rapid the turnover of the pond waters through the unit and the greater the kill of microorganisms each day but the less exposure time for the microorganisms to UV irradiation. If flow is too fast for a given size unit, then the efficiency of the kill declines expediently. Thus, the pond owner obviously must take into account all the factors that effect efficiency of UV irradiation on a particular system and use judgment to adjust the flow rate through the system for best results. I have found that slower is always better when in doubt. 

 If water passes through the unit too fast, that is above the manufactures limit; it will be useless at killing any microorganisms at all and algae will only be flocculated. The flocculation process involves the optimization of the electric charge of the algae and bringing floc particles (Flake of precipitate that comes out of solution during the process of flocculation.) together to form larger particles that can easily settle in a sedimentation chamber in the filter or get caught up in the pre-filter filtration mats themselves. Be careful in the UV units you buy because sales wording of the unit may indicate that the UV unit is not meant to eradicate bacteria or algae but only floc it. These floc UV units are usually cheaper and go under the name as UV clarifiers than UV units that can eradicate pathogens go under the name UV sterilizers. Most manufactures will state what their UV units are for. 

Properly run UV units will prevent ponds from having bacteria blooms, effect redox and TDS for the betterment of the pond, and keep our aquatic animals in a more suitable and stable environment without the excess of microorganisms.

UV Clarifiers and UV Sterilizers are not equal in what they do and use different types of UV lamps.