Here are some construction photo's. The tank was built, established and then pulled apart about 4 months later and redone. The original design did not have any area beneath the land section for the fish. Now nearly 100% of the tank bottom is available to the fish and stingrays.
This is the main waterfall early in it's development.
Early design of the front river section. Back then all the land was elevated to keep the substrate out of the water column but not accessible beneath.
The early theme was going to have a fallen log as a focal point.
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This shot shows the land area after the substrate was added.
And then I did the redesign to elevate the land and make all of the bottom accesible. First I gutted it.

Then I built a platform to hold the land area above the water column.

Test fitted it into the tank and covered with permeable landscape fabric to keep any substrate out of the water column.

Added the hardscaping.
Then did some of the early plantings
Ta-da- An elevated land section with plenty of caves and hiding areas for both the Poison dart frogs on top and fish beneath! Both sides of the tank were done in a similiar fashion on separate occasions as the stingrays and all the fish were still living inside the system during the reconstruction.