One thing to consider when you see very fine "particles" in front of the light at night is that if you have a SWCG, ozone, or any significant aeration, they are just as likely bubbles, not particles. Some times I turn my light on and things are perfectly clear, then the SWCG cycles and I get millions of little tiny hydrogren bubbles. You can't see them in the daytime, only at night with the light on.