Many people use their aquariums as a focal point in a room. In hopes of adding to the interest of the conversation piece, some fish owners will place found objects inside the tank as decoration. While this may give the fish tank a truly unique look, it can also be very dangerous to your fish.
First of all, found objects are usually not clean. Bacteria is not the only problem as chemicals like cleansers, petroleum products, or other toxins may have been used on the object and still be present. It may be difficult to fully cleanse the item from potentially hazardous residues.
Secondly, certain objects may degrade or dissolve slowly, in the water. If an object softens in the water, the fish could nibble at it, making them sick, or it could release toxins into the tank. Plastics, for example, generally release chemicals ever-so-slowly into the water.
A third concern is the pH level of objects one might place inside a tank. Maintaining the proper pH level is very important for the health of your fish. Surprisingly, even objects that seem natural to a fish environment, like shells, wood, or coral skeletons can negatively affect the pH of the tank. The concentrated environment of a tank does not allow for some items that may not affect fish living in streams, lakes, or the ocean.
Finally, items that are found can have rough edges, sharp points, or potential trap-hazards for your fish. A rough item may be fine for a while, until something startles one of the fish and it injures itself against a rough edge. Items that are manufactured specifically for decorating fish aquariums are the safest choice, when creating the environment inside your Biube or Biorb fish tank.