I have to agree that a new person to fishkeeping would almost certainly not start with a 6 foot tank. However, I admit that it is possible, so here are some references that would be helpful to you or others in your situation:
Here is an old thread I liked on cycling. If you are having nitrite problems in a week old tank, then your tank is not "cycled" in the same sense that others are talking about. It is a long post, but very well worth reading to someone unfamiliar with the concept of the nitrogen cycle in a fresh water aquarium. Most of the links in this post are not good though, since it is so old.
<a href="http
/www.fishforums.net/content/Tropical-Discussion/10099/http-www-fishforums-net-index-php-showtopic-10099/" target="_blank">http
/www.fishforums.net/content/Tropical...howtopic-10099/</a>
That thread touched on the idea of fishless cycling. For more information on that, see this thread:
http
/www.fishforums.net/index.php?showtopic=113861
Here is an excellent thread about weekly maintenance on your new tank. Following something like this will help avoid problems in the future, after your tank is cycled:
<a href="http
/www.fishforums.net/content/Tropical-Discussion/171045/http-www-fishforums-net-index-php-showtopic-171045/" target="_blank">http
/www.fishforums.net/content/Tropical...owtopic-171045/</a>
Lastly, I wanted to address the statement:
"i asked the guy at the shop before i bought them he goes siliver sharks do grow but he goes like any fish if the tank is big enough and got room it will grow bigger "
This is a common misconception. Fish that are supposed to grow big should be big tanks. Most people who think they will only grow to a size good for a smaller tank they are in do not know a lot about fishkeeping. As a result, the fish are usually stuck with water quality problems due to improper maintenance,
and a small tank. Together, this sure does stunt their growth well. It is not good for the fish though.