I have a 3ft community set up. I have noticed in the last couple of weeks that there has been small white bunches of a cobweb type substance growing from the gravel upwards. Although i recently added some new live plants the problem started just before i got them. The fish and plants are healthy and water quality is ok. The light is on in the tank for ten hours a day. I have never come across this problem before. Any advice would be most gratefully received.