I'm using the sterilizer to purify the water from pathogens and help clear the water, also it helps with general water quality...this is not a big U/V Wattage it's a green killing machine rated for a 40 to 50 gallon aquarium. I
I'm have been using u/v in my freshwater tanks for years... I was just wondering about the effects of using it in saltwater aquarium
From what I’ve studied it’s all about contact time and if you want to kill of certain parasites, like for example ich, you have to achieve 72000 micro watts/sec and there is a calculation you can do based on the UVC power and the flow rate to achieve this.
The UVC only kills things that pass through it, so of course it’s not 100% effective but it certainly helps, and in reality I can’t see any down side to using one other than changing the bulb every 12 months.
The following is a quote from DD (David Saxby’s company) which I found helpful when researching:
‘’For water clarity we suggest a U.V intensity of 30,000 microwatt's/sec/sq.cm and our U.V sterilisers are designed to deliver this at the quoted flow/contact rate through the unit.
The mistake that many hobbyists make with our and other manufacturers U.V systems is not getting the flow rate right through the UV and connecting any old pump to it.If flow is increased the bacteria/algae or parasites do not get the correct U.V exposure and many happily pass right through the unit.
This is of some interest when trying to kill the white spot parasite as a greater U.V intensity of 72,000 microwatt's/sec/sq.cm is required to kill it. So with this in mind we have to take the standard flow rate of the unit for 30,000 microwatts and divide it by 2.4 to give you a flow rate for 72,000 microwatts exposure time.
So you will need to divide the suggest 500l/hr flow rate by 2.4 giving a new flow rate through the unit of 208 l/hr to kill the white spot. This will give a 0.6 times turn over for a 350l aquarium so it maybe worth going for the 20 watt unit and running it at 416 l/hr giving you over 1x tank turn over an hour but giving the correct kill intensity for white spot.’’
Wouldn't it just be easier to use non-euclidian geometry or fuzzy set theory? 
jk.
