@ mere
I have the same plant in my "feeder" tank as you have in your smaller tank, and it spreads like wildfire, I'm constantly cutting it back and your larger tank looks stunning.
attached are some pics of my 2 tanks and my axie, my axie tank in in my bedroom, It's not usually lit as she hates the light, and as a result the java fern I got for her tank was not doing well so I put it in the other tank. the axie tank is pretty boring right now, but she does not mind, she rearely ventures into the middle of the tank and she just trots around the sides anyway and it seems to work well. when I find some nice rocks for her tank, ill add them and a nice piece of wood that I have to go in aswell, but when we moved into our house, we had all the gardens torn up, so as a result we have no rocks at all laying around.
the other tank is set up for white cloud minnows, its planted and it has really taken off, its been only 2 weeks since I planted it. that tank has lots of water movement, it has a hang on the back filter on full and a sponge filter with air being pumped into it rather vigorously, I have a strong current to keep gunk from building up on the plants, and it seems to be working. and for good measure, I had to also share some photos of my axie.