As a underwater photographer, I would suggest getting a better camera 1st rather than moving your fish into different tanks.

If you have a DSLR try getting a macro lens + CPL filter (get rids of glass reflection). Then turn off the lights in the room but keep the aquarium lights on. Results will be the same if not better, since you get the feel of a "natural" environment in the pictures.

The more you use the cam, the better value it is And for underwater shots, I use a Canon S100 so a step lower than your GF2 !

As a comparison, by investing in a good camera you'd be able to capture any memorable event, take it everywhere and shoot anything. Compared with a "photography" tank which will only be able to hold fish for short periods without a filter system etc.

A camera capable of taking good aquatic photos can be had for ~RM1k. (ie: Canon S100, G10 etc). The difference between the pro equipment (Canon 1D X + 400mm F2.9) is the chances of getting a good shot. With the 1DX and a good lens you're pretty much guaranteed a printable shot on the 1st try. But with cheaper cams, it takes a few more shots but you'll get there after a few tries

And yes, I do have 1Dx + 400 2.8