?? not sure what you are not understanding. Essentially in my current viv the bottom substrate is all gravel. The gravel layer comes to just above the normal water level for the part that will be the land area. On top of that I currently use a combination of that pressed spagnum moss and ecco earth. The part that I want as water areas has the gravel at varying levels to give the frogs a choice of shallow or deep.

When I finally get motivated enough to build out my exoterra viv, then I'll pretty much do the same except for I'll use the LECA for the lower layers that will be covered up by whatever will be my dry substrate for land. I'll still use the gravel as the top layer in the wet areas as the LECA just doesn't look natural. There will probably be some barrier such as landscape cloth or nylon screening between the LECA and whatever layer is immediately above it. It may not really be needed but it will also act to keep the finer substrates for falling down into the LECA and keep the LECA from migrating up.

Water will flow into the pond area via a water fall or stream and the return water will be picked up at a distant point under the land part. I feel this will encourage bacteria and other biological growth that will help with water quality, as well the roots of any live plant that I plant.