Ok, here is my 2.5g FW
tank that sits atop my cube at work. It has 4 Fancy Male Guppies in it. No heater, just a Duetto 50 Filter that also aerates the water with a little snorkel on it. I never asked the boss to see if it was ok to set it up, but so far, the only thing anyone has said was that it was a great idea! I actually started with a discarded old glass punch bowl. That broke when I was cleaning it one day, so I went a bought this little rectangle one. I am right next to the copier, so people stop to look at the fish all the time. It has become quite a popular item.
I used flattened glass marbles as the substrate, but I am finding that uneaten food and poop ends up collecting down in the cracks. I am wondering if I should swap that out for some of the extra gravel I put in my new planted tank at home. I have been able to use a turkey baster to "pump" water through the marbles to get the junk floating and let the filter pick it up, but does anyone have an opinion on this, other than how it looks?