Get back in there and change more of the water - with levels like that, 30% isn't going to help enough. Vacuum the gravel while you're at it.
Your tank
is still cycling, when the bacterial filter is fully established you'll see ammonia and nitrite levels of zero. Anything above zero is harmful to the fish, so you may need to do large water changes, daily or even twice a day, to keep the levels down. As long as you're not exposing the filter media to chlorine, water changes won't prevent the biological filter from continuing to develop.
Adding a little salt to the water will help the fish cope with nitrites, but add it with caution, just a bit, and dissolve it before you add it to the tank.
I'd stop feeding for now, or feed very little once every other day, until the tank settles - food will only add to the ammonia that the filter is trying to cope with.
Good luck, I hope you can save him.
[edit] just saw your post, sorry you lost him
[/edit]
