One caution on clarifiers.....this is one product that can make matters worse if you overdose!. They will cause small particles to clump together if you dose properly but if you overdose they will cause the particles to go into a colloidal state that your filter cannot remove! I personally don't like them (except for the chitosan based ones like SeaKlear, and even that usually is not necessary)

Since you have a sand filter, adding a bit of DE to it will probably do a much better job than any clarifier can!