Review on Laguna PT492 Biological Bio Max by Heather Johnson

Less than 350 grams, you get a lot more for your 4 pounds. There are also more openings for good bacteria. I used it in my pre-filter and in my waterfall filter. You'll save a lot of money when you buy Revain pond equipment. It will cost you a lot more to go to a pond store or a fish store that sells pond equipment for a lot more. Also, they come in a mesh bag that prevents them from floating. I can only recommend them and will buy them again next year.