I have to check into exactly what type of sand I have, but I've the same exact cats in the same tank. I know it's the coarser, bigger type of sand, as I tried regular sand and it was too easy for them to "sweep" around and get into the sump. I loved the bare bottomed look, but the sand helped to keep the water chemistry neutral for them to thrive. Like I said, I have the "heavier" type of sand in my tank for them...btw, my profile pic shows an older picture of the cats with other inhabitants who are no longer in there, but the sand's the same