With long-term use, mudballs (SS lumps) are formed in the filtration layer,　and water is formed,　and the filtration gravel at the bottom is spouting out.

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Reasons for the non-landing phenomenon of filter media (example)
By repeating a series of states as shown in the figure below, water is gradually formed over several places,　and madball formation　and non-landing phenomenon occur. In addition to this, water may be formed due to defects (clogging / damage) in the lower water collecting part,　and a non-landing phenomenon may occur.

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About the possible harmful effects of the non-land phenomenon

Decrease in filtration capacity
● The original effective area of the filter is reduced　and the filtration capacity is reduced.
● Water concentrates on the part with low filtration resistance,　and the raw water slips through without being treated.
● The time during which the differential pressure rises becomes shorter,　and the quality of treated water cannot be maintained unless the frequency of backwashing is increased.
● Outflow of filter media

Effect of filter body
● If the supporting gravel layer collapses　and reaches the lower water collecting device, the water collecting device will be clogged, causing damage to the water collecting device　and outflow of filter media to the treated water side.
● Destruction of water collector