I have bio balls at the bottom of my tank for my turtle to play with. He spends a lot of time rolling them into different formations. https://www.amazon.com/Bio-Balls-Filter-Media-Aquarium/dp/B07YM1RHSQ/ref=sxin_22_pa_sp_phone_search_thematic_sspa?content-id=amzn1.sym.b7aa28ba-e8be-499b-b539-5135fbd84ece%3Aamzn1.sym.b7aa28ba-e8be-499b-b539-5135fbd84ece&crid=88L3DODSNPYW&cv_ct_cx=large+bio+media+balls&keywords=large+bio+media+balls&pd_rd_i=B07YM1RHSQ&pd_rd_r=9d4f0c6d-e89c-4ec8-b57f-ecc0eba4b9a6&pd_rd_w=NbOZv&pd_rd_wg=dWrEm&pf_rd_p=b7aa28ba-e8be-499b-b539-5135fbd84ece&pf_rd_r=GPVNHZB5S8P1GXNMBJ0Q&qid=1679082089&sbo=RZvfv%2F%2FHxDF%2BO5021pAnSA%3D%3D&sprefix=large+bio+media+balls%2Caps%2C107&sr=1-1-2b34d040-5c83-4b7f-ba01-15975dfb8828-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzNkEzS0xFNlM1QjJHJmVuY3J5cHRlZElkPUEwODAzNTUyMkM1MkpWVUIzS1JNTiZlbmNyeXB0ZWRBZElkPUEwMDY2NDMzMU1VMk83WUI2Vk5YVyZ3aWRnZXROYW1lPXNwX3Bob25lX3NlYXJjaF90aGVtYXRpYyZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=