I have had this planted tank setup for just over a year now. When I started the Tropica Soil sloped towards the back of the tank. The front was about an inch. The carpeting is Dwarf Sag. The substrate now looks as if it is about 4" deep, but this seems to be made up is the roots of the Sag,
The tank overall is stable. No algae it any other nasties. What advice can you give? One thing comes to mind is to remove the Sag to trim its roots and possibly add some new substrate. It looks like it is pot bound if that term can be used for aquatic plants.