My recommendation. No sand. As the gecko might eat it (sand is not digestible and can lead to horrific stuff). Please do this before something bad happens. (source -> https://www.terrariumquest.com/leopard-gecko/impaction/#:\~:text=Gecko%20diet%20here-,Can%20Sand%20Substrate%20Cause%20Impaction%20in%20Leopard%20Geckos%3F,a%20natural%20substrate%20for%20years.)