Sea water will not fix film in any way whatsoever. Household ammonia can partially fix film, but is very very slow IIRC.
Pool Chlorine eliminator which contains Sodium Thiosulfate will work, but is hard to get. Ammonium Hypo used as fertilizer, is a very good fixer if pure enough.
PE
Pool Chlorine eliminator which contains Sodium Thiosulfate will work, but is hard to get. Ammonium Hypo used as fertilizer, is a very good fixer if pure enough.
PE


which