those white worm things are most likely planaria worms. They won't harm your fish (feed on bits of uneaten food... decomposers). They most likely came in with any feeder fish u may be used.

Once u clean out your filters and the tank bottom, their numbers should dwindle.

Only effective way I know of getting rid of 'em is thru the use of a drug called praziquantel (aka Droncit - Dog deworming tablet brand.). However, since planaria will not harm your fish, I suggest not to bother with medication.