BC- Hang in there. This is a very rewarding hobby. Personally, I think your salinity is low, but that probably doesn't account for the deaths. I would suggest a skimmer as it is a good safety net (I run one on my 180 that has 270 lbs of liverock!) and I think that most people on this board run one inspite of the "skimmerless" hype. What is interesting is your nitrite level. That should read 0 for sure. If the nitrate cycle is complete, ammonia is converted to nitrite which is then converted to nitrate. In an established tank, ammonia and nitrites should read zero.
I would also suggest getting a sand bed. They have done wonders for my tanks. Do alot of research on skimmers before you buy. There is alot of junk out there.
Continue with the water changes and your maroon clown may make it. They are quite hearty. Please realize that you are not alone. I killed a few fish myself, and have made many mistakes.
Let us know how things go, and we will be willing to help with any other questions, especially about skimmers!
One more thing- don't take the posts here too seriously. Many people on this board feel compelled to flaunt their "knowledge" in a way that is sometimes demeaning. I know I have been guilty of that once or twice myself.
Good luck.
E