Why does my water smell bad after the water softener?
It sounds like it's an activated carbon filter, which takes organics out of the water (like the sulphur smell), and that it needs to be rebedded (this needs to happen typically once every 3 to 5 years, depending on level of contamination). Once the activated carbon is 'used up', it actually becomes a good breeding ground for bacteria and is worse than completely ineffective. (Aside, this is the same reason that jug-style filters like Britta need to be replaced regularly -- and it's better to use nothing than an old one). 






There is not really anything called an "iron filter". Softeners can low levels of iron out, and greensand filters can be used for higher levels, but a greensand filter will have a small tank attached with potassium permanganate (dark purple stuff) in it: