Lizzie is according to my vet, is right between a juvvie and an adult. I want to put sand in the tank. I want to go with play sand. Does anyone think this will be a problem or should I wait till the end of summer, as this is what my vet told me to change diets?
Any sand you use comes with the risk of impaction, even as adults, so I would advise against it. Tile is a fantastic substrate, it's cheap, looks good, and is easy to clean. It also comes with no impaction risk and won't grow bacteria, so it's hygienic.
I would talk with your vet about it. Using a loose substrate responsibly takes a bit more effort than a solid one. You have to be super on your game as far as all the other aspects of care (lights, heat, diet etc) rather than just size/age if the dragon.
I use loose substrate that is a sand/soil mix but wouldn't use plain sand. You need to consider keeping it clean as well as how it will benefit you dragon. Play sand offers very few benefits but several drawbacks.
The Facebook groups advancing herpetologial husbandry and reptile and amphibian bioactive setups are excellent resources to browse for ideas. Many keepers in these groups have kept their dragons on a soil mix from when they were babies.
In addition to the maintenance drawbacks of using sand in a captive environment, loose sand doesn't really replicate their natural habitat very well. It's much closer to the bioactive setup that Taterbug is describing. They live on hard packed clay with grasses and leaf litter rather than loose sand. I don't have room for a tank that can have a proper bioactive substrate so I try to imitate this using ceramic tile (the hard packed clay) and small fleece blankets or scraps to provide some relief to the hard surface and allow digging and burrowing the way the leaf litter would. It is quite easy to clean and keep sanitized which is important in an artificial environment that is smaller than their natural habitat.
Video to show the hardness of the ground (I'm NOT trying to crush the ant and it passed unscathed) https://vimeo.com/165385899