I need to buy some activated carbon granules for a water purifier (aquired it FOC but without any carbon ). The only granules I've seen for sale are 3mm in size and are being sold by weight. I can easily measure the volume of the purifier (at a guess I'd say about 10 litres), but I have absolutely no idea how much a litre of dry 3mm carbon granules weighs.
Can anyone tell me the weight of the granules and the best place to buy them from please?