What's happening to my Gramma?

[Breadbox]

So I've noticed some tiny white spots dotting across the tail and pectorals fins of my gramma+the occasional flashing behaviour.

I didn't notice much/anything yesterday before it must have just appeared recently, I'm not noticing white spots on the body expect for possible splotches of discolouration(which might not be anything at all) and his behaviour appear completely normal, swims normally and eats without problem. All my other fishes do not have any symptoms.

I'm suspecting Lymphocytis here but all images of the disease show big white dots on the edge of the fin while my gramma has tiny white spots all over the fins.

I do suspect my coral beauty have the disease however, as there seem to be some specks of tightly clustered white dots on top of her frontal dorsal fin that grow more obvious with time.

What is my gramma suffering from and what should I do Sorry for the bad quality, this is the best my phone can manage. There is a cowfish suffering from similiar symptoms in the thread below mine.

 

[Breadbox]

Another question is on Lymphcytis, if my angelfish or gramma is indeed suffering from it, what is the best course of action?

I've heard 'pristine' water condition and good food with vitamins. Now what qualifies as pristine water condition? Low suspensed bacteria count? Low nitrate or some other dissolved substance? Or it suspended particulate matter?

My aquarium water is not clear at all, it is full of tiny mysterious white particle suspension that I honestly have no idea what it is and the filter isn't picking them up. Ammonia is non exsistent and API nitrate tests gives me a 0-10ppm result. My water is slightly cloudy(even ignoring the previously mentions white particles) so I suspect there's quite a bit bacteria in the water.

I also have difficulties with feeding "good food with vitamins", I tried feeding frozen hikari food with vitachem supplements but liquid vitamin don't seem to seep into the frozen mysis too well, plus, frozen mysis is filthy and a huge contributing factor towards the floating particulates and cl water I suspect.

Should I soak flakes and pellets in it? And is there some simple food that skips all these hassle and doesn't cloud the water?