I meant the snails or shrimp for the 1g, but there is no reason you can't put them in all of your tanks if you like them. If you are not overfeeding, they are not supposed to multiply into the millions, maybe we could say that is a good indication of a problem?!!? You could run the 1g filter on the tank for a while, along with whatever comes with the new tank, assuming it doesn't seem to bother the fish. He should be fine with a little extra for a couple of weeks. Or, if you can, incorporate whatever filter media ( and the gravel too! ) from the 1g into the 5g, with just the one fish, that should be enough to keep the tank cycled.