Biologic evolution

The transparency of seawater in the water tank went up after a day.
I thought that only this was different by one pipe.
You only had to notice early.
When the water current flows to the filter under the water tank with the
pipe and the water current flows from the filter by it toward sand, this
experiment is a success.
Even if the experiment succeeds, a useless thing is thought by breeding
of the shellfish.
This is not understood if it doesn't try.
The softness of sand is softness for the finger to stick easily, and for
the finger to touch the filter.
This is according to the image.

When the fisherman became winter it, the motive of this experiment was from
a story that the littleneck clam was not able to take it.
The sand of winter seems to be hard.
The fisherman｢Do in my power?It is not possible to take it. ｣It grieved.
As for the state of the sand of my water tank, when the amount of sand is
large, sand has become hard.
The finger did not enter sand.
This?
This is a motive of the water tank redecorating.

The doubt whether sand becomes hard when winter comes boils why.
Do because the water temperature falls when winter comes?
Do because the flow of the current changes when winter comes?
Do because the water level falls when winter comes?
Do because the quality of sand changes when winter comes?
Do because the direction of the wind that blows to the sea changes
when winter comes?
Do when winter comes?
When thinking oppositely
It becomes an idea of ･････････ ? with the coming of summer.
The answer is not understood no change of the aspect.