A clogging indicator for a fish tank or aquarium comprising a transparent
vertical tube with a float positioned therein. The indicator is designed
to sit on the outside of the tank and the filter itself. The water level
in the tube is lowered and raised according to the amount of water with a
rear chamber of the filter. Indicating marks are located on the tube to
visually display normal or clogged operation. Backup water from a clogged
filter will raise the water level in the rear chamber and thus also the
indicator tube. As the water level rises, the float raises toward a
warning indicator mark to indicate the need for filter changing.