How do these pests manifest on inverts and how can a new guy
, I'm one, know what to look for in a QT?
You won't see any ich manifestation since it wont infest the inverts.Without a fish if there happens to be a viable cyst it will perish after "hatching".
There are a number of threads on the sps forum replete with pictures ,observations ,treatment options and symptoms for the others.
Infested corals exhibit bite marks, recession and ultimately death. Some red bugs can be seen on some of them,Flatworm damage usually shows up in "bite marks". Monti nudibranch are visible to the eye and just strip the monti of tissue ,sometimes very rapidly. All of them can spread throughout the tank. There are many other infestations that can be spread by new coral specimens as well.