Using the "Burn" tool to isolate an object from the background. With the settings shown on the picture (2, 3, and 4) the tool (5) will remove light colors but keep dark ones.

Rubber feet of a tripod.

A typical head of an inexpensive tripod.

2 of the tripod's legs can be shortened so the camera is very close to the tank glass for extreme macro shots.

2 of the tripod's legs can be shortened so the camera is further back from the tank.