[MassiveDynamic17]

I'm going to build an undergravel filter for a 10 gallon shrimp tank. I was thinking of putting netting between the bottom layer and the substrate (to keep sand out of the UGF).

What kind of netting is good? And doesn't dissolve in water over time?

 

[Diana]

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.