Thank you for your question. Most of the bacterial additives are comparable. There is not one that is considered "the best" as different people have different experiences with different products. We recommend the Water Repair Series: Colonize. We have provided a link to this below.http://www.drsfostersmith.com/produ...
For established aquariums the dosage is as follows:
To maintain clean water and proper biological filtration, add 1 teaspoon (5 ml) of Water Repair Series Colonize for each 10 U.S. gallons (40 L) each week. 16 oz treats up to 960 gallons. 64 oz treats up to 3,840 gallons.