I always keep this on hand for adding new water. Since it is concentrated it doesn't take much to do the job, the bottle will last a long time. I use a pipette to dose the minimum effective amount since I learned from Cory that it takes some oxygen out of the water as it works on the chlorine. Using minimal effective dose means minimal oxygen loss, while also being more economical.
Very good product! Quick delivery!
I use this every week during water changes.