I have , had them in my newly set up quarantine tank. I noticed a small amount only where the light hits the glass near the corner. I do not illuminate the entire tank. I squashed them with my finger & I have not noticed any since which was about 2 weeks ago. I do see string like projections in that same area , not sure if its algae or newly forming ones on the glass? I use sponge & internal canisters on that tank. I read they are in the water supplies & if nutrient levels get higher enough they will form. Certain meds , do your HW can kill them as well as lowering nitrates. Come to think of it when I first saw them I had high nitrates, since it was newly cycled with ammonia. They were higher than 40 ppms when I noted them. Now I am below 30ppms last time I checked & I do not see any at the moment. My other planted tank I have a case of white worms which are dinitrius in nature . Sorry about the spelling. I know they are living in my substrate even though my tank looks great. They could be causing a nitrate spike which I am currently trying to figure out. I read flubinzole will kill them & is ok for most shrimps. That was my best shot at your problem.