I'm using the Bio Sea Marinemix and love it. Tried the Marine Environment type also once but went back to the Marinemix. As for the difference in packages .... it is just how they are packaged. You can buy 150 gallons worth .... cheapest if you order it when it comes in one single bag - or you can get it 3 bags (of the 50 gallon mix) or 6 bags (of the 25 gallon mix). I have purchased both the 150 gallon mix in a single bag (cheapest way) and in the box that comes with 3 of the 50 gallon mix bags. For me, the single bag works well since I mix more than 50 gallons worth when I'm doing changes on both my 300 and 90! And I have not had a any problems at all with their salt clumping up or hardening up after opening the bag.