this is beautiful omg, how big is it?

aaaa thanks. It's 135 US gallons / 520 litres

Do I see rainbow fish in there or do my eyes deceive me?

But gorgeous natural setup!!

Yup. I have a few. They're mostly the leftovers of the big group I used to have so they're all old kiddos. Bosemani, banded, blues, dwarf neons and uhh female Parkinsons I think? I've never properly ID'd those guys but they match the shape of the male so I'll just assume that. I used to have reds too. Pretty babs.

May I ask what you do about CO2 in your tank? I've made several attempts at planted tanks in the past and have used "bottled" CO2 to very limited success, and the plants have always ended up deteriorating rather than thriving. I recently officially gave up on a planted tank and spent ridiculous amounts of money on fake plants to try to replicate such an environment so that I could enjoy my tank and focus on my fish without the worry of keeping plants alive, but planted tanks are just all around superior and I hope to try again one day. Maybe next time with one of those fancy, big CO2 systems.

I've never bothered with CO2 systems. Just keep the tank super aerated with strong light and a decent current- all things I mainly do for the fish tbh. I will say though these plants aren't particularly old.