A microscope may help in parasite identification. That is assuming that you have fish big enough to do body scrapes, etc.
However, to actually see anything, you need a pretty good microscope. The "toy" ones won't have enough resolution to show much. <It is not the "power" that is inadequate, but the optics. Cheap scopes have a lot of distortions & most things come out as a blur.> And of course, you need some experience to do wet mount, & maybe staining, etc. <A first year university Microbiology course will help!>
Getting a scope will be educational & interesting, but don't expect good clinical diagnosis without training.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.