Yeah, I don't like those fountains either... let me see if I can get you a link to the calculator. One possibility for the w/c is to keep the fish in a bucket of the old water, empty the pond, clean it, but don't refill it quite yet. put the bucket in the pond, and slowly add new water to the bucket. let it over flow into the pond. when there is enough water for the fish to swim in the pond, put the fish and his bucket water in the pond, and slowly continue adding water until it is full. This will make it a lot harder to dechlorinate, though...