Too much Nitrite and Nitrate in tank

Question
I have a fairly new 28 gallon freshwater tank.  It has been doing fine until about 3 weeks ago.  The nitrite and nitrate are very high and I have tried several things the pet store recommended.  I have changed 40% or more of the water.  Still it is not coming down.  I have lost 3 fish already and 2 more are not looking good.  I don't know what else to try.  Any suggestions?

Thanks

Answer
Kim,
in the situation that you are in you almost have to continue on the water change your way thru it mentality.
Feed the fish only once and at that not a lot. You want to cht down on the amount of pollution in the tank.
You could add some stress coat and make sure the temp is correct.
Short of starting over, thats about all you can do. If you lose the fish, just let the tank idle for a few days untill it settles down.
What you have to watch for is secondary problems due to the stress of the original issue.
If you have additional questions, just ask