I haven't had luck finding an answer to this question and the Search feature on this site just gives me a localhost error. I've read that many use a large bucket to do a water change. I'm assuming you would then just fill the bucket with new water to the level the water was at after you were done removing tank water. How then do you know how many gallons are in the bucket to ensure the right amount of chemical to de-chlorinate the water is added? I actually don't have any empty gallon containers to re-fill the bucket. I guess I could use 2 liter bottles and do a liter to gallon conversion. How do you all do it?