tank has fungus??? help asap!

i came home after being away the last day and a half, and found that my tank was filled with tiny white particles drifting through the water and collecting on my ornaments. I had noticed these a few days ago, but being a newbie i thought they were just waste, as there didn't seem to be too many. Today there are many more and my fish are less active than normal. also by looking really closely i noticed a very fine web of white threads on my gravel. What do i do to get rid of this....i just almost lost them to nitrite poisoning and now this

did 50% water change which did absolutely nothing

by inspecting closer, i've figured out that the little white particles are MOVING!! they're stuck to the side of my tank and drifting thru the water, about as big as the dot on this !
WTF!!!!!!!! please help

by moving i mean that they're like tiny worms, moving on the side of the tank