i HAVE TWO IN A 20 LITRE TANK (1 WEEK) SAME PROBLEM THEY DONT MOVE ABOUT AND THE FEMALE WONT EAT ,today they have started to move about a bit more ,i was also thinking of adding another female .Last week i got 3 small panda corys to clean tank and perhaps be a kind of dither fish .One died within 24 hours ,the second i found dying with a bite out of his tail ,i removed the third .All my water readings are ok .As you say ,in the shop they were buzzing