I know my jar of Fivestar Super Moss says to rehydrate it in a small amount of cooled wort. I tried using some of the local spring water I was brewing with in one of the Tostidos dip jars I store washed yeast in. It def doesn't mix that easilly. So pre-dissolving it in some cooled wort will def help when it's time to add it to the BK. In the case of the super moss,1/4tsp dissolved in some wort 10 minutes left in the boil. It def helped clear my PM beers nicely. Particularly since I top off with gallons of cold local spring water that's been in the fridge 1-2 days...sometimes more till I get a whole day open to brew PM. The chilled water drops the temp about 10 degrees pretty quick,so the super moss can help more cold break settle out in the fermenter.
Regular irish moss preperations use 1/2tsp 15 minutes from the end of the boil.