What is the definition of external tank?
it is space shuttle
first the rocket boosters carry it into space then the external tank pushes the shuttle above earth then when the shuttle is ready the external tank falls off and the shuttle is ready for its mission then after its mission the shuttle lands and blows out a parachute come out from the back to help the shuttle slow down.any parts from the rocket or shuttle can be reused except the external tank.
The difference between external filters and internal filters is the quality of water cleanliness. An HOB (Hang On Back) filter can do a great job on a small tank that is not over-stocked with fish provided you take proper care of your tank; many people run more than one HOB on their tank depending on the tank size, and the fish. External filters are much larger, typically sit on the floor beside the tank, or…