The 3x5 Photo Tank holds fish (like small sunfish) which are too large for the Micro Photo Box. It also holds several micros at once, which makes it much easier to compare several similar looking fish. Also, with more than one fish in the tank, they seem to settle down more quickly so you can get better photos. Molded from a single piece of plexiglass, it has no seams to leak. The hinged lid will keep fish from jumping out. Inside dimensions roughly 3.5" x 5.5" (3" front to back).
Please note: The manufacturing process creates a very thin (almost unnoticeable) scratch at the extreme right and the extreme left edge of the front and of back faces. You would have to look hard and in perfect light to see them. I do not think they will show up in your photos (they never have in mine).
However these "imperfect" tanks have more noticeable scratches or have a minor imperfection in the plexiglass. They are brand new and never used, but they aren't perfect.