Overall there is a significant reduction in the flatworm population. Some spots that were completely covered in them are flatworm free. I added 4 of them and I can still see 2 of them. The largest one disappeared for a week in the same little hole before coming out and vacuuming the little red devils up again. They do move slow, and they do what I can only describe as suicide in a reef tank. They move up the rocks hunting, and when they get to a crest, instead of crawling back down......they just release off the edge. You can see where this would be a problem with powerheads and anemones. So if you get them...I would say a few weeks of no strong powerheads would really help. Not sure what you would do for an anemone though. For the most part, they stay in the open. I don't really think they are more active at night or during the day, but I can usually spot one or the other out on the sand or on the rocks. I did find an egg sack, but I am not sure if it is fertilized or not.