So I took George's advice (thanks George!) and pulled all the E Tenellus out and kept the least 'algead' plants to start a new carpet and threw the rest away.
After the suggestions from the what to do next, I've also added another couple of rocky sections to balance out the main caves on the right. So this is what it looks like now....
(180 litres, 120W lighting, Pressurised CO2, 10KH, undergravel heating, aquaclay substrate with Florapol and pea gravel)
Here's the overflow tank too. It's a low-tec Rekord 70 with a pair of killis and their offspring in it. I think overgrown is probably the best word for it
Although there's a lot of growth in there transplanted from the main tank, I've been surprised how well stuff grows in here, albeit a lot more slowly, I guess having a rich substrate and primarily rooted plants helps. If you look closely you can see the amazon sword variety in the front has a long runner going from it to the back left of the tank where a new plant has started.
(70 litres, 30W lighting, aquaclay substrate with Florapol and pea gravel)
After the suggestions from the what to do next, I've also added another couple of rocky sections to balance out the main caves on the right. So this is what it looks like now....

(180 litres, 120W lighting, Pressurised CO2, 10KH, undergravel heating, aquaclay substrate with Florapol and pea gravel)
Here's the overflow tank too. It's a low-tec Rekord 70 with a pair of killis and their offspring in it. I think overgrown is probably the best word for it

(70 litres, 30W lighting, aquaclay substrate with Florapol and pea gravel)