1 pump per 10 gallons of water once a week for low to medium light tanks (and double the dose for medium to high light tanks)
For a 55 gallon low light tank, that means one bottle will last you about a year. If your aquarium has medium to high light, then dose two to three times a week. The key is to use a test kit to measure your tank water and aim for 10-20 ppm of nitrates. It’s as simple as that.