Update: Both my moors are now dead
Dont know what went wrong, just hope that my other fish will be alright now.

When I first started out with fish I was in the pet shop about twice a week for around 6 months asking questions and getting all the knowledge that I could and it was under their advice that i had 2 fan tails in a 3gal tank and again they told me that i could add several more fish to my 35litre one. I have been acting on their advice from the start so do you think that they are giving me the wrong advice on everything??
I do around a 30% water change once a week, vacume the gravel and do a general clean/tidy once a week. I use the API master test kit and the readings are normally bang on, got an ammonia spike after adding the new fish but it calmed down after a few days.
I am going to go back to the pet shop (Pets at Home) and let them know what has happened so hopefully they can prevent it happening to other customers.