There are lots of information and theories about these diseases. Folks on this forum have way more experience than I do, and they know what they are talking about, but there is such a thing as perspective. I would say on a positive note that you don't have a huge mature system with lots of livestock at stake (but we all hate it when a fish dies). I, for one, am leaning to the school of thought that there is no such thing as an ich free system. It can come in on frozen food, frags, fish etc. Keep stress levels low. Doing too much may make things worse, but there are things you can do short of a QT. I don't want to make strong recommendations on things that "might" work, but if you do some more research you will find some things you can do to at least help the situation if it gets worse. I recently had a bout with something similar. Things are better for now. Time will tell, and, your mileage may vary...
https://www.reef2reef.com/threads/is-it-ich.442136/