Germicidal UV dose table shows the UV dose needed to inactivate germs
www.americanairandwater.com
quote from above article:
"Please note that many variables (air flow, humidity, distance of microorganism to the UV light, irradiation time) take place in a real world environment that make actual calculating of the UV dosage very difficult. However, it is proven that UV light will kill any DNA-based microorganism given enough UV dosage. UV breaks down DNA on a cumulative basis. Therefore, as air circulates through the ductwork of an HVAC system containing an UV light, the UV light continuously disinfects the air. If a microorganism is not effectively deactivated on the first pass through the ductwork, the UV light will continue to break its DNA down on subsequent passes. Microorganisms do not sit in a static environment in HVAC systems except on coils which can be exposed to UV light also. Microorganisms multiply rapidly if not controlled. The UV light helps to reduce airborne microorganisms from the indoor environment."
I recognize the above was written with concern for the sterilization of air, but air is just a different type of fluid and I believe the statements are just as relevant to water.
So , assume the following:
UV device holds 1 gallon of water,
return pump operates at 125 gallon per hour,
therefore, each gallon of water is exposed for (60minutes x60 seconds)/125 gallons=
28.8 seconds per gallon per hour
Now, assume the return pump operates at a flow rate of 10x per hour,
therefore, each gallon of water is STILL exposed to 28.8 seconds per hour
60 minutes x 60 seconds = 3,600 seconds
3,600 seconds/10 = 360 seconds per cycle
360 seconds per cycle / 125 gallons = 2.88 seconds per gallon per cycle
2.88 seconds per cycle x 10 cycles per hour =
28.8 seconds per gallon per hour... imagine that
So, single cell bacteria that replicate every 20 minutes are exposed and sterilized once every 6 minutes preventing rapid reproduction, and
Multi-cell parasites are exposed 28.8 seconds per hour x
(? hours to replicate{I know, I don't have this value yet to complete the calculation}) and sterilized preventing their rapid reproduction.
Also keep in mind that almost all of the devices used for aquariums use the same UV replacement bulbs.
So, I suggest you opt for the highest wattage unit you can find and set the return rate for what you require for your filtration. The UV will only affect the organisms found in the water column. So, only the free swimming parasites will be rendered sterile, but that's still good, and bacteria and algae in the water column will be sterilized to boot.
My belief is that many of the vendors of these devices fail to recognize the fact that aquariums are closed systems and cumulative exposure due to high turnover rates is just as effective as one time exposure when no turnover occurs (as in municipal and industrial water systems.)
