I always wondered why I never see any mention of folks using sand as the media in flood and drain systems. I'm presuming sand is cheap, widely available, has lots of surface area for beneficial microbes and would present little mechanical resistance to growing roots. I would welcome anyone's thoughts on this subject
I have not tried sand in aquaponics but I have tried to use it as a substrate for a planted aquarium. The problem I had was not being able to adequately clean the silt out of it. The water stayed "muddy" no matter what I did to clear it up. A courser sand might have worked but would have been hard to find.
Don't use it.... it's just too fine... clogs... and needs regular cleaning as mentioned... and to clean it, you basically need to take it out, clean it, and then replace it...