I put in the hydroballs mainly for the filter, I didn't want to clog it with gravel. I've found some of the hydroballs will float. I covered that "layer" with a substrate barrier then put gravel on top. The green part is gravel from a previously established aquarium which I put in there to help break down any waste products. But most is large gravel "river rock" which I thought was big enough not to be a danger to the frogs. I do have quite of bit of java moss in the water section which would inhibit swimming. Again, it was put in there mainly to help with breaking down any waste products.

Their "first" setup was a Lees Herp Habitat (with an elevated land area) where I had 2 inches of water around the bottom plus rocks to climb out of the water. They did not seem to like being in the water without being able to touch the bottom and stayed mainly at the water edge around the rocks at the bottom. In this setup I've seen them spread out in the java moss, or "buried" a bit in the water with their head out.

But I could try building up the land area more so that I can add more water, which would make it deeper.