Aquarium water conditioner question

Many of the aquarium water treatment products use sodium thiosulfate
to remove harmful chlorine/chloramine. But some products also bind the
ammonia that splits from chloramine into a harmless compound, which is
still available to plants and bacteria. Does anyone know what the
chemical is that does this? I would like to make my own water
conditioner. The thiosulfate is easy to get. But I need to know if the
ammonia eliminator chemical is readily available.

Thanks,
Dave

.