Is that a ladder type diffuser? If so I would recommend removing that and replacing with an inline atomiser or a reactor - less clutter in tank and better co2 dissolution. Tbh though plant growth looks very healthy so It might not be best to fiddle with co2.
The hairgrass needs to grow and cover the foreground.
As for hard scape, you could remove the mopani wood and get some nice rocks to nestle amongst the foliage or remove mopani and go for a full dutch style.
Congratulations on a very healthy tank, I look forward to seeing it become even better!