I use API Bio Chem Stars for my biological media. Originally I had all of my 141 stars in my AquaTop canister assuming API's claim that 1 star covers 5 gallI use API BioChem Stars ons of water. But I read in an article recently it's more like 1 star for 2 gallons meaning 150 stars would be required to cover 75 gallons (my tank size). So I purchased and ordered more stars just in case. I now how 159 stars in my canister.