I guess a good question might be... are the worms kind of short and fat/flat? And really small?
Or long and slender? And kind of... well... long?
Short, fat/flat and small points to rhabdocoela flatworms. Not always harmed by treatment to get rid of planaria.
Long, slender, and... once again, long... that could be detritus (swims like a snake if in water column), nematodes (squiggles...) or possibly some other worm.