+1 Add it when it's ready to boil. I started out adding the recommended 10 drops for a 5 gallon batch.....and am now cutting back to find the actual needed amount. What's strange is that on my last batch, without thinking, I mistakenly added the recommended dose (1/4 tsp) for 5 gallons of 5-Star's Super Moss, evidently the concentrated active ingredient (carrageenan) in Irish Moss. Stranger than that......it worked in preventing any kind of boilover. I only thought about it later. Never even got the Fermcap-S out of the fridge.....
“Malt does more than Milton can / To justify God’s ways to man”
-A. E. Housman (1859–1936). A Shropshire Lad , 1896.