I actually like the way you have the wood framing the mountain here... and the wood is very dynamic with an interesting flow. The mountain just needs to be planted. Using similar planting from the right would bring in even more cohesion, although you could use a different stem plant for the background
Lastly, you might consider letting the soil behind the mountain on the left continue to rise toward the back of the tank (pushing a few of the stones towards the back as well so the mountain appears behind the wood portal). This would help improve the perspective. If possible, move/adjust the intake(?) in that corner to allow the deeper soil.