Pretty much agree with Duane. I've used it at times over the years and found benefits with no downside, apart from whether you consider some additional electricity use to be a downside. There's some debate over dwell time/wavelength/intensity, etc., with, for example, one self-appointed, online 'aquarium science' expert citing a reciprocity rule in photobiology, which basically says that the cumulative effect of repeated low dose exposure is as effective as higher dose exposure. Sounds impressive, no? Not only that, but, in theory, with the repeated exposure of high water turnover through it, you could use a relatively inexpensive unit and be in good shape, a notion I've seen mentioned elsewhere-- heck, I may have believed it myself at one point. However, upon doing some research, I found it's more complicated than that. The proposed "law" has been questioned and not always proven true when tested-- basically, it may (more or less) work in some cases, but not very well in others. This points to what Duane says, it can be effective on some pathogens, but it's not a panacea that covers every possible issue, depending on things like wattage, dwell time, wavelength, the particular organism, parasite, or pathogen in question, etc.
