Quote Originally Posted by tim_bessell View Post
Sea water?
Doesn't work. Has been proved a few times and is what led William Fox Talbot(i think?) to go to Herschel about his problem and he suggested sodium thiosulphate (hypo)

If you had a store and too much money to burn, bog standard fish tank dechlorinater is sodium thiosulphate (though not the Tetra branded stuff apparently). I found at Wilkinson's(UK chain of cheapstuff stores) they have small vials of this in the pet fish section but it works out to be quite pricey compared to buying normal raw chemicals (2 for about 25g maybe?).