For your 55 it would be 25 ml for initial dose, or after every large water change, (5ml for every 10 gallons). Then 5 ml per day, or every other day, (5ml for every 50 gallons) So it would be 25ml + (5ml x 6) = 55ml per week for daily dose, or 25ml + (5ml x 3) = 40ml per week for every other day dose. For a 250 ml bottle, that is 4 1/4 weeks for daily, and 6 1/4 weeks for every other day.