A tank been setup for only a week is your problem, no bacteria growth and fish constantly producing ammonia.
Take a look at the pinned section on fish-LESS and fish-IN cycling and you will understand more.
thankyou very much just a fyi the guy at the fish store said u should have alot of fish they will die but it will speed up the process faster were no fish it will take a while
LFS (local fish stores) tell you what you want to hear, and what will make them the most money.
You NEED to go to the beginners section, and take a look at the pinned articles about fish-in and fishless cycling like said above.
Fish produce ammonia through respiration, left over fish food in the water and fish waste in the water.
What ever the case is, if you have fish in a tank, you are going to have an ammonia source.
The only difference is, how much ammonia fish can tolerate.
Any ammonia reading over .25 ppm is going to give the fish permanent gill damage, and will eventually kill them, as you unfortunately found out.
In a fully established tank, there are what is called autotrophic bacteria that live in our filters that process ammonia, so that the ammonia reading on your test kit will zero.
When these bacteria process ammonia, the ammonia then turns into nitrite, then there is a second type of bacteria that process nitrite in nitrate.
There is no kind of bacteria that process nitrate, and the only way to get nitrate out of the water is through water changes.
Now, all of what I just described, takes place in a fully cycled/established tank.
Where am I in all this?
You are at the beginning with no autotrophic bacteria present in the filter.
How do I get these autotrophic bacteria?
If there is an ammonia source in your tank, then these bacteria will eventually start to colonize in your filter.
How long does it take to colonize enough bacteria to process all of the ammonia that my fish are producing?
It will tank on average, if done properly, 4-6 weeks.
Now, there are different ways to do it, the two ways are called fish-in, where as the second way is called fishless.
Have a read about them in the beginners section so you can fully understand how these two processes work, and feel free to ask any questions you may have.
-FHM