The more I read about Gammarus and Hyalella the more confused I get. I don't know how you distinguish one from the other. Various species of Hyalella are found from northern South America to the Arctic, while in North America, Gammarus are found mainly in the eastern US and in the Midwest. Yet I've read articles that appear to contradict all of that. I can't recall seeing any article that discussed both Gammarus and Hyalella. It may make no practical difference if they are the same thing or if there are hundreds of species within each genus scattered all across North America. For me, it's learning from the experience of others and trial and error. FA, Daphnia, diatoms, and detritus (leaves especially) seem to go well with scuds. I've read that pH should be kept above 6, and they should be kept cool and well oxygenated.
