I've just started to keep tropical fish and have opted to start small and build on it. I did all the right things by setting my tank up and putting the water in it then setting it running. I left it for a week as I was advised to do so before I started to add my fish. Now as I am totally new to all of this I decided to just get 5 black neon tetra to start with and a rainbow shark... the shark was the fiance's idea! Well everything has been fine for the past 5 days with the fish in the tank and when I got up this morning and went to feed the fish and turn the light on I discovered that the water is ever-so-slightly cloudy..... is this normal and if not what could have caused it and how can I cure it