water in tank never looks clean

Question
we bought a hexagon small tank 30 litres and we had 2 shubukins in there quite happy ,we had a elite filter and that was it , we then added 2 goldfish (1 Orange , 1 White) i was distraught to come home and find that the orange goldfish had died , i panicked told my partner to clean the tank as he usually did but to do it asap so that the fish dont get sick and it seems the other 3 are ok , i then decided to buy a 3ft x 1.5 tank (aquarium) my partner set it up it came with a fluval plus 3 filter and air pump , all was great but i am clueless as to why after just one day of the water looking lovelly and clean to it looking cloudy and greeny looking , we made sure the gravel was thouroughly washed , we,ve never used ammonia or nitrate we just put in the new tank "tap water crystals" and we change the water every 2-3 days !!
the fish are fine and are happy but its not nice looking in a big tank like the one we got and it looking dirty we do regular water changes but its a pain having just one day of it looking clean
i love the way a tropical fish tank is set up it always looks crystal clear but my partner says they are very hard to keep and besides that ive gotten attached to my shubunkins
Are tanks normally like this ?
Is it just tropical fish who have the crystal clear water ?
sorry ive gone on a bit im just a bit baffled and searching on the web i get so many different opinions and i never find the right answer to my question
would very much appreciate your advice we are in the uk
regards clair

Answer
Hi Clair;

It's just too new to be stable yet. It's still in the break-in period and it can take 6 weeks or so to complete. You started off with some pretty messy guys, and a lot of them too. Change no more than 25% of the water every 3 or 4 days, but don't disturb the gravel or the filter. The beneficial bacteria that grows in there to start handling fish waste hasn't had a chance to grow enough colonies yet. Read through my article on new tanks to help you learn more about the break-in process and what's been going on in there;

http://www.xanga.com/Expert_Fish_Help

At Your Service;
Chris Robbins