There is a product called PolyFilter ( it's a pad for a HOB filter) which takes out medications from water. It may be worth getting one to see if that solves your problem in the long term. Carbon filters should help take out the smell of sulphur ( I am on well water which stinks and use a carbon filter for our drinking water and there is no more sulphur smell.) What you may need to do is set up a holding container to prepare water to use for water changes and such so that you have instant access to good water. A RO filter may help as well. Check with the manufacturer to see if it removes sulphur as I am not sure of this.
On a side note, sulphur used to be used as an antibiotic for both humans and fish and a little sulphur in the water may actually help keep your fish healthy. Eventually, however, the fish diseases may become immune to it's properties so other meds would need to be used should your fish get any condition that requires an antibiotic.
Hope this helps
