I have had large out breaks of black leeches. I also had them crawl to the water surface and die. They are only in the gravel. I have not been able to get rid of them 100% I found one again yesterday. So I am guessing they are loaded in my gravel again. I was going to do my weekly vac today. I removed the towels I keep on so the direct morning sun does not reach the tank. When I removed the towels I found what looks like worms and egg sacks. They were not there at midnight but were at 9am. I do feed California black worms and have for 3 years with no problem. I bred them and they do not look like what I now have in my tank. The leeches have never bothered the fish. But I think they riddle the planted bulbs. I don't know what to treat all of this with or what these orange worms are. What ever they secrete the leech also show the orange slim on it. I really need idea's for this problem.