It seems that last Saturday, not only did we introduce new guppies and white cloud mountain minnow to the tank, but we also introduced white spot. We only still have 2 out of the 6 guppies and both of those are covered with white spot, one of the dannios is also showing signs of irritation.
We have been out to the fish shop this afternoon and the tank has now been treated. We have to repeat the treatment every 48 hours until the spots are gone and then for a further 48 hours.