I've viewed my tank kinda the same way I've built home made macro cameras. Use two large (3"+) magnifying glasses.
Hold the first one so you get a clear image, but upside down (about 3" from the aquarium wall). Then use the second one anywhere from 6"-14" from the first one to inver the image back upright again. Now play around with the distance of the first one from your subject, and the second one from the first until you've got a super sized image.
Now you've got yourself a large sized low power microscope
I've also used the macro extension tube on my SLR digital camera to take a close up photo, then look at it enlarged on the computer monitor to see detail I couldn't see otherwise. Changing the levels in photoshop can bring things out you can't see as well.
Was able to identify a 1/8" sized coral hitch-hiker 20" from the front pane of glass this way