Sorry to hear about the kitten and the fish.
I also bought some goldfish not too long ago (four juveniles - each less than an inch long [tail not included]) and after a week and half, lost three of them in the span of four days. All four were infested with Ich, and all of them contracted secondary infections.
I read some advice somewhere (here on AC?) that fish hobbyists should do what reptile keepers do and just assume that any new purchases are infested with parasites and are diseased. I'm beginning to buy into that line of thinking.
For what it's worth, the next time you purchase goldfish, you might as well buy an Ich treatment and a broad spectrum microbicide (like Triple Sulfa) too and give them concurrent treatments. I know I will...