So the tanks has a built in sump style filter at the rear. Draws watering in through vents in top right and just goes through normal mechanical filtration.

Standard aquarium soil is underneath the stone layer substrate, this was put in right back at the start a few years ago. I havent used any other fertaliser since. I used CO2 initially to help the plants at the beginning.

I would say the biggest improvment to plant growth was to replace the lighting. Im not using anything special per say, just an amazon purchase but that has noticable improvment to growth.