I'd like to add that i still continue to do my weekly water changes and test my waters chemistry as often as i always have, I have seen UV devices sold in pet stores that state less regular water changes will be required (this should be a huge no no)..
The UV has done a far supperior job on helping me rid the tank of whitespot (and alot less stressfull on the fish) than medication was "medication and high temps alone failed to shift it".
How does the UV sterilizer serve only as a cosmetic fix that clouds the underlying issue as im sure anything that can aid us to keep our aquatic life in good health has to be a bonus and i will be most certainly keeping mine, other than whitespot (no fish loss) this is the only health effecting issue ive had.
We use co2 in our aquariums to aid with plant growth, aquatic plants can and will grow in aquariums without us adding it ....... but its nice to have and certainly does make a big differance, the same goes for UV we can look after our water and fish without it but its nice to have and does certainly help..
The UV in my case was bought to assist me in clearing up the whitespot as chemical treatments were proving not only stressfull to the fish but also useless against the strain in my tank, using only hight temps and the UV i have not had a single fish showing any signs of infection.
BTW.
I dont have marine, this is installed in my tropical freshwater set up.