If I didn't know better I would say there is a spider web in my tank. It's attached to a small white cone that is maybe 3/8's of an inch long and it looks like there is something inside. The opening in the cone is maybe1/8th of an inch wide. Any ideas?
There are worms that live in tubes (vermiteds) that put out a "spider web"(mucus traps) like substance to collect food from the water column. There mostly ok, some folks have had trouble with them when there reproduction gets out of hand. If you get to many just break them off to get rid of them, but just a few you should be fine.