What sand for my fish tank?

I have 2 African Clawed Frogs(Albino) I dont know how big my tank is. It's just bigger than a 10 gallon. I have a filter and heater and some plants. I have gravel and some big pebbles o the floor of the tank. But i want sand because they can swallow the gravel and plus sand looks better, but do i need to buy sand from the pet shop or can i use sandbox sand which can be cheaper?