At the advice of our vet, we use a product called Sand Clear. It is more expensive than the other products mentioned, but our vet feels it works more effectively (and I don't buy it at the vet's office- so there is nothing 'in it' for the vet). I have also used Metamucil and had two come down with mild sand colic. So, I am back to Sand Clear and have had no other problems. I feed it for one week every month.