Correct Uv sterilizer wattage

[madrhino]

Hey guys,
What is the correct uv wattage I should be running for a 125 reef tank with a 30g. sump. Right now, I have a 9w. csl double helix. i've done some reading and it seems in a marine tank this may not be enough. Some people recommend at least 25w. for my setup. Should i invest in another unit to bring the wattage up?
Thanks!

 

[JeremyR]

FWIW, the coils in the double helix are plastic. While CSL says the coils are a UV safe polymer, they did admit to me that the fittings in some of the early double helix units were not uv safe. Regardless, I had someone bring in a 36w unit where either the coil or the fittings inside failed, it leaked, and burned out quite nastily. It did not trip his circuit, and was plugged in live and burned out for some time before he noticed the little blue light wasn't on.

 

[SAT]

Most manufacturers recommend 25W for a 125G. That's typically based on a dosage of 30,000 mws (micro-Watt-seconds per square centimeter), a flow rate that passes all the water through the unit every 3 hours, and a one-year-old bulb (which typically has 65% of its orginal output and is near its end of useful life).

You should consider why you're using UV, however. If the intent is to kill most common bacteria and algae spores, that dosage will do so outright. However, many protozoans (e.g., Crypto), viruses, and fungi are harder to kill. To kill Crypto outright, you need about 400,000 mws.

The good news is you don't actually have to kill Crypto... you just need to damage its DNA so it can't reproduce. You can probably do that with 100,000 mws. Or you can accept that it will take several passes through the unit, at 30,000 mws, to do the job. You then need to ask youself how much time you want to give those little suckers to find a host.