< preamble > Not sure if this belongs in physics, chemistry or engineering. I feel sort of silly, because I should know this. I'll probably do a face-palm when I get the answer. < /preamble > My pool has gotten cloudy so I've thrown some chlorine in. This killed the bacteria allowing the filter to remove it, and my pool is now clear. I know what the chlorine does; it causes the bacteria's cells to rupture, killing them. My question: What is it about exploded bacteria bits that allows the sand filter to sweep them up? My first hypothesis: The filter is actually not involved. Suspended bacteria are significant in size enough to cause cloudy water. Contrarily, dead bacteria dissolve into their comiponent parts (various gases, ions, salts) which, being much simpler molecules or even atoms, go into solution. As solutions, they are transparent. i.e. the components of the bacteria are still there (though now harmless), but they no longer affect the clarity of the water.