Type of filters

Sub gravel filters
Hidden below the sand level, these catch the dirt and concentrate it in one place. The top sand appears clean, so does the water, but the dirt is still there in the tank until and unless you remove the whole filter and siphon off the dirt.


Corner filters
The biggest hoax ever made on the unsuspecting aquarist. The filter is small, neat and cheap; it is so small that it becomes saturated in an hour or two and after that you are just fooling yourself.