Hi, thanks for the reply Caryl! Unfortunately the tank didn't come with the old media so we had no choice but to buy new media. I've put the fish back in their old, smaller tank, put the smaller tanks filter media into the new tank to help promote the cycling and covered the tank with a doubled over blanket. Will see how it looks in a couple of days and do the 50-75% water change you've recommended. Living in Auckland city we don't know of anyone nearby who would have daphnia, but thanks for the suggestion