I'd appreciate any thoughts or input on the following options under consideration.

The source is a private well, relevant water analysis is

Calcium 64ppm
Iron .05 ppm
Manganese 0.28 ppm
sulphates 84 ppm
hardness as Calcium Carbonate 307 ppm or nominal 18 grains/gallon
TDS 578 ppm
pH 8.02

Untreated water will have a distinct H2S odour about 3 months after annual well chlorine shock treatment.

Current system is a Star water systems Ultra Pure 11 filter, this uses air injection followed by a 100 gallon air over water contact tank before the filter unit which contains a Birm, Calcite mixture. Claimed to remove iron, manganese and H2S. It doesn't work!!!! I notice Star no longer sell this system. The contact tank is an old galvanized tank and will be replaced whichever option below is chosen.

Following the star filter is a conventional softener and finally a UV sterilization step. Softener works fine. Drinking water is by RO unit on the softened water stream, no problems with this.

House has 3 full bathrooms and 3 half baths but 95% of occupancy is only 2 people.

Maintenance is normal replacement of RO fiters and membranes, salt replenishment, annual well and whole system shock chlorination.

PROBLEM: Occasional slight H2S odour from none RO softened cold water. occurs about 3 months after shock chloination. I'm convinced the H2S comes from iron or sulphate bacteria which re-populate the well over time following shock chlorination and which the Star fiter system, Birm active ingredient, will not remove.

Solution alternatives currently under consideration.

Option 1 the lower cost likely workable

Remove the star filter, the air injector and the old contact tank and install a Greensand filter with Pot. Perm regeneration, then continue to existing softener etc.

Option 2 the highest cost, Bullet proof??

Remove the star filter, the air injector and the old contact tank and install a proportional chlorinator followed by a new 120 gallon contactor tank, followed by a nexsand filter then a carbon filter then on to the softener etc. Possible use of a magox inplace of the nexsand filter.

Comments on the above would be appreciated and any other alternatives gratefully received.