Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
A fine netting like the material certain (very fine) fish net is made of might work. Look in fabric stores for nylon in the right mesh. Polyester also holds up just fine.
Cotton will rot in the water. Slowly enough, it is not a problem, but then your net is gone.
Depends on what size your sand particles are, you probably should get a sample of the cloth (look in the remnant bin) and test it.
Many years ago I got a 90 mesh nylon fabric for straining honey. Held up just fine.