I need some advice about my cold water fish tank - I bought the 60L tank to upgrade from a starter tank. I had 5 leopard Danio's after loosing a number of fancy gold fish. i evenually introduced 2 fancy goldfish with the danios after getting advice from the pet shop. My tank was great for a few months, but i got up one morning to find both goldfish dead. I took a sample of my tank water to be tested and was told it was perfect to keep goldfish in and the guy couldnt help on why the fish had died. I did change the bulb a short time before this happened, when i bought the bulb the package said it was a tropical bulb but the lady in the shop said that it would be ok for a cold water tank ( it has a slight pink glo). In the following months i had a number of fancy gold fish and within a week or so they all died. I noticed that the danios seemed to be bullying the fancies so i took the danios out of the tank. I bought 2 fancy goldfish and after 2 weeks they seemed to be doing well so i bought 2 more. It is now about 2 weeks since getting the last 2 fish and they have all died one by one.I part change the water in the tank about once a fortnight and also change or clean the filters. Can anyone please let me know what i am doing wrong.