Diabolix

Hey guys, bit of an odd question. I have a 200L tank with an ornate bichir, an albino bichir and a chocolate talking catfish. From time to time I feed them a school of feeder fish, as well as the usual beef heart , shrimp and carnivore type pellets. The tank is stable, weekly 1/5th water changes, 2 internal filters as well as an under gravel filter. The tank is also planted with a variety of unknown but hardy plants (the survivors of a mixed bunch from animates). Lately I have noticed what appear to be like water fleas, small white dots which buzz around, land on the glass and filters and crawl around, before zipping around the tank again. In addition to these, generally near where the prolific areas of animated white dots are, are what appear to be very flat planaria which crawl around on the class. The volume of these critters seem to be increasing. Now in an aquarium with smaller fish I would imagine at least the white buzzing around critter would get culled pretty quickly. My questions are 1) Anyone else had these show up? 2) Anyone know what they are? 3) Are they detrimental? Cheers