How to clean minutes sea shells from shell grit.
I know how hard it is to deal with tiny shells that are less than 2mm. I use needles of all sort but the best one is the acupuncture ones and it will take care of little grains of sand that are logged in the aperture and siphonal canal.
To get rid of sand inside the shells, I put a shell one at the time into a small sealed plastic bag then with my fingers I flick the shell and all the sand will come out leaving a shell free of sand.
If the shell is very fragile make sure you flick the plastic bag and not the shell.
You can see all the grains of sand are gone from inside the shells using that method.