Ponds tend to accumulate lots of dust, dirt, leaves, bugs and other debris.
In a well-designed system, this debris and organic waste is removed from the pond by a filter.
The beneficial Bacteria in the pond filter process the dissolved
fish organics. This is done efficiently in the presence of well-aerated water.
In a pond with rocks in the bottom, there are many places in the rocks and gravel where organic debris gets trapped
and hides. As the debris becomes deeper the water flow through it begins to slow, and the debris begins to rot.
If this isn't cleaned thoroughly each year you will end up with a toxic cesspool of dead and dieing fish.
A pond without rocks on the bottom is easier to clean, and easier to maintain.
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