UV Sterilizers

by Nate Santora | June 6, 2012

For every new aquarium hobbyist there are a few trials and tribulations that will occur. New tank syndrome, faulty equipment, bad advice or unhealthy livestock. In this entry I want to focus on a piece of equipment that will help keep your animals disease free. If you have not read our article, “Don’t Buy Sick Fish” check it out first. It covers how to properly select healthy fish.

It is not unusual for new aquarists to spend a lot of money on fish and coral only to lose some or all of them due to an uwanted pathogen that was accidently introduced into the aquarium. For those who have had enough of playing russian roulette with their aquarium inhabitants a UV sterilizer might be the answer. UV sterilizers have a germicial lamp that disinfects water passed through it.

UV sterilizers will eradicate parasites, bacteria, viruses, fungus and algae spores. There is some misinformation as to whether UV sterilizers can kill parasites such as Cryptocaryon Irritans (marine white spot) or Amyloodinium Ocellateum (marine velvet). Parasites occur in three stages. The reproductive stage, the free swimming stage and the parasitic stage where it is attached to fish and seen as a white cyst. Properly sized UV sterilizers are effective against parasites in the free swimming stage.

The UV sterilizer size and flow rate are based on the target organism and the size of your aquarium.

Target Organism = Cryptocaryon Irritans (marine white spot)
System Volume = 100 Gallons

Calculate the flow rate required to pass the entire system volume through the sterilizer twice a day.
Fo = flow rate
9.2 = purity coefficient @99.99%
G = system volume in gallons
T = time in hours

Fo = (9.2 * G) / T => (9.2 * 100 Gallons) / 12 Hours = 76.7 GPH

Next find the zap dosage required to kill the target organism.
Cryptocaryon Irritans (marine white spot) = 280,000 µWs/cm²

According to the Emperor Aquatics website a 40 watt UV sterilizer will provide a zap dose of 180,000 µWs/cm² at a suggested flow rate of 157 gallons per hour (GPH). Is this sterilizer large enough to kill the target organism requiring a zap dose of 280,000 µWs/cm² at our calculated flow rate of 76.7 GPH? A little math will help us find the answer.

(180,000 µWs/cm² / 280,000 µWs/cm²) * 157 GPH = 100.9 GPH

This tells us that we need to decrease the flow through a 40 watt UV sterilizer to 100.9 GPH to achieve the desired zap dose of 280,000 µWs/cm². In additon the minimum flow rate (76.7 GPH) for two system turnovers a day has been met.

Investing in an UV sterilizer is well worth it when you consider that it may be the difference between buying your fish once versus having to replace the aquariums entire livestock population due to disease. It is worth noting that the sterilizer is not a cure all but a tool to help prevent disease. Severely infected fish cannot be expected to survive by adding a sterilizer after the fact.

If you would like more information or help sizing a UV sterilizer for your aquarium please contact the store.

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