we only used 7 or 8 drops due to the water displacment with the live rock and sand, that may be why not all of them died, siphoned them out as they died and as i saw them floating. will try to wait a couple of days and try again. So you think we should use the 20 drops? think we have around 15 or 18 lbs of rock in there.. if thats the case then I think 20 drops will surely kill them all