Depressed to have to wait to add a new fish?...No, I learned my lesson. I had a beautiful reef, and I didn't quarantine...well I got fish that had the ich parasite. It was my 90g tank, and the fish were too large and too many to be placed in a hospital tank, If I could afford another 90g it wouldn't have been so bad...but a 20g wasn't going to work.. I lost a few fish, but the remaining fish managed to fight off the parasite and survive. I ended up not being able to add new fish for 2 years (now that's depressing), because all new fish are stressed, and stressed fish get attacked right away with the parasite, then the numbers would be bad enough to re-infect the healthy fish that were fighting it off. I did add some cleaner shrimp, they like to pick the ich parasite from the fish' gills, that gave some relief to my surviving fish.
All that grief could have been avoided if I had only quarantined that one little new fish.
The reason you I think you had no problems just before you changed the water, is because you have a good sized tank, we keep telling folks that the larger the tank the easier it is to keep up...well you added 5 new fish all at once. If you had not had the large tank you did, you would have completely crashed the tank. The water change you did do, probably saved the more hardy fish that were able to survive.