Hi All, can anyone help. I am a newbie to fish keeping. Set up tropical tank (40 litres, internal filter, live plants) cycled and water tested all ok. After only a week added 6 cardinal tetras, fed small amount of flakes once a day.fish were fine for a week then I carried out a 25% water change! chlorinated and added filter boost to the new water before adding to the tank, the next day noticed 3 of the tetras had white spot. Unfortunately my store did not have white spot treatment in stock so I increased the temp to 28c and added 2 tablespoons of aqua salt (as advised by the store) and unfortunately over the next few days lost all 6 tetras. I am afraid to get any new fish as the white spot may still be present/active in the tank. Is this possible and if so how can I get rid of this?