I am wondering what is a symptom of ich cause my fish sometimes shiver either they sometimes do it at the bottom against the gravel or at other levels to but they don't do it a lot only sometimes but enough to cause som concern.
I saw pictures of fish with ich and it's like BettaCouple says, like tiny grains of white sand or salt are stuck to their skin. Difficult to spot if your fish have marbled colour patterns like mine, I guess.
Do your fish also seem to rub against objects (or the glass), as if to scratch an itch?
What fish do you have? Livebearers? There's that shaking disease I read about. Let me think. That's it: shimmy. Perhaps you could look into that?
P.S. I actually thought one of my fish had ich and I looked closer. Luckily, it was just tiny water bubbles on its fins. It just had had a bubble shower.