Calcium liquid isn't absorbed as effectively as dust. I would get some calcium powder, here is a schedule for it - http://www.frogforum.net/food-feeder...schedules.html

As long as the pebbles are big enough that the frogs cannot fit them in their mouth, that is okay, if they can fit in their mouths, you could have a problem there. Personally, I have a water area that is 4 inches deep for my greys and have found them to be great swimmers. It has river rocks so that it gradually gets deeper, making it easy to get out, and there has never been an issue. I have heard that whites are fairly good swimmers also. I love water features, but make sure all your pumps and filters are easily accessible for maintenance. Nothing like having to tear apart half of your viv because of a sputtering pump.

This thread may be worth reading through to help fine tune things with your first viv - http://www.frogforum.net/vivarium-te...ion-101-a.html

In both of my tree frog tanks, I have branches in there but have a vine suspended across. Make sure everything is really secure, whites are heavy and will only use a branch/vine that feels stable to them.