That Java Fern my man...
Looks absolutely fantastic - the only thing I'm finding off is the tall Ludwigia (I think?) near the cave, I'd either trim it down to get it bushier or underplant it with some crypts or something like Juncus Repens to make it look less leggy.
Wills
That's a co2 indicator, it's a good way to work out if your levels are right when first setting up the co2 so to not out too much in, or not enough.Very nice aquascape! I'm new to fish tank stuff but I'm considering doing this kind of aquascaping stuff. What is that weird bulb thing with green liquid? Also what is the powerhead and filter style called?
I haven't thought it before but will keep an eye out for them now and have a look.Congo Tetras would be great in this tank. Have you thought about Black Phantom Tetras. I always think that the combination of Congos and Phantoms work well.