A couple of different things, jor. What ich med did you use? For tetras (and some other fish) you have to use a half dose because they can't tolerate a full dose. Did you complete the medication, using it for....I believe 10 days is the gold standard, before starting the salt? I doubt that the frequent water changes stressed him out, fresh water is always good for fish.
Wait for someone more expert to come along about what to do next. I don't know if you can treat a fishless tank for ich or if you will end up having to nuke the whole thing.
Don't get new fish until this tank has been treated or nuked. Then read the links on here about fishless cycling. Although I've never done a fishless cycle, it is said to be easier on the fish. You have to be patient though, with or without fish, it can take up to six weeks, sometimes longer before your tank is cycled. Even then, you can't go and buy ALL of the fish that you want at first, you have to add just a few at a time. And make sure that you don't overstock. Make sure that you choose the correct fish and the right amount for the size of your tank.
You may have learned by now NOT to listen to what they tell you in the pet stores. They'll tell you that if you buy (insert product) it will instantly cycle your tank. Not true. They will tell you that you can put lots of fish in your tank and it is big enough. When I first started I put four goldfish in a 15 gal tank because I was told it was big enough. Well, a 15 gal tank isn't big enough for ONE goldfish. So, I got them a bigger tank but still wanted to use my 15 gal. I fell in love with black (silver?) tipped sharks. I was told I could put six in a 15 gal. Thinking I was being safe, I only bought four, only to find out that they need something like 70 gal PER fish! So make sure to do your research and know what you want to put in your tank. Its hard though. You go to a pet store and absolutely fall in love with something, they tell you its a good fish for your tank, you buy it, find out it will need a bigger tank. Then you think that you will upgrade "someday". But things happen, someday never comes and you end up with a miserable, sick or even dead fish!
Patience, patience, patience! Read, research, learn, ask! What size tank do you have? Do you have a test kit? Were you using Prime or another dechlorinator when you did your water changes? Did you make sure that the new water going into the tank was the same temp as the water in the tank?
Ok, enough with the novel! Someone more expert than I will come along with more advice for you, I"m sure! Good luck.
