I had been buying Zoo med hydro balls made for terrariums* and this gardening stuff is cheaper. Would it be safe for potentially using it for a frog tank?.

*I bought two bags thinking I would use two bags for two terrariums, a third extra bag later and I still need more for just my 40 gal terrarium. So I guess I need four or five bags of this stuff per terrarium. Considering I want some in my anole tank and am setting two more terrariums, costs go up fast.