all I will say is that since I added UV lights to my two main tanks a few years ago, I don't think I have ever had a problem with discolored water, nor with sick fish
the one time I had some fish that did get sick, it was concurrent with my UV light being disconnected and I didn't realize it . . . fixed the light, and since then all is good
also, never had any luck with fish spawning before the UV lights, but have seen success since . . . again, might be other factors, but I'm happy with the results