I just bought a 5 lb pail of Sodium Thiosulphate for the pond/aquariums. The
instructions I have read here in the past suggest that this should be enough
to dechlorinate lake Superior. But reading the bucket, it states that I need
anywhere between 1/4 tsp and 1 tsp of raw ST per 5 gallons of pond water.
This means that a 250 gallon water change would take up to 50 tsps. Given
that the bucket only contains about 5 cups, that's 10 water changes.

The stuff in the bucket looks like some sort of crystal, not a powder. Has
this stuff been bound with some other chemical to reduce it's strength? At
this rate it's no cheaper than the generic slime coat. Bummer.