I use buckets for water changes. Even though my buckets are 5 gallons, I only fill them about half way due to lifting restrictions. I dose each bucket for 5 gallons. I figure if I do 4 half buckets and forget to dose one bucket (which does happen to me) I'm still ahead of the game. Of all the money I've put into my setups over the years, dechlorinator is one of the lowest priced items I use and a large bottle lasts forever.