Chloramine is chlorine gas injected into dilluted ammonia. Really diehard stuff (10+ days to try and outgas) and unless you're dealing with large amounts of water (+100's gallons added per day) then vitamin C (ascorbic acid or sodium ascorbate) is exponentially cheaper.

I have been using this stuff https://www.amazon.com/gp/product/B00FG6XXWU/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1 for a few years now.

6ml:40 liters is sufficient. I believe that's 1 teaspoon to treat 10 gallons. A 1 gallons bottle should be enough to treat 6,500 gallons of water so its not too bad of a price.