I like a gravel substrate for FH's, and they do too !
Let's all be honest here, the fish enjoy sifting through it, digging in it etc. V3nOm, I can see from your picture that whatever fish is/was in that tank also likes digging, judging from the pile at the front. Why remove something that improves their quality of life.
Personally, I also like a black background for FH's too, faders and otherwise .... so long as you have decent lighting.
I think your tank is just a little full (that is if there is a big fish in there now (I can't see one at all!)). For a bigger fish I'd remove just a bit of the decor, and arrange the rest more in the middle, or in a sort of strip from left to right, again in the middle of the tank. That still gives maximum swimming room around the outside, around the front back and both sides of the decor. Also something with a bit of height ... either a plant or a bit of wood ? .... near the centre of the tank is nice to my eyes.
Also, you could try some of the plastic plants that stick on to the back of the tank, made for vivariums ... they look great in aquaria too. I have used them for ages, as have many others with no problems,, so no need to worry about chemicals leaching from the plastic.
I can't stand all these empty, bare-bottomed tanks. The reason you see bare-bottomed tanks is for ease of maintenance, not because the fish actually prefer it that way.
Just for interest here are my current setups. One 150G set up for a big fish. Hopefully you can see what I mean about setting the decor up in a strip from left to right in the centre of the tank, leaving swimming room all around.
Then theres an 80G split in half for two grow outs. I would like a black background in the 150G too, and I tried it, but the fish goes nuts at his own reflection in the back of the tank. It was very stressful for him, so the tank remains background-less. It's not too bad though as there is a plain white wall behind the tank, so as long as I keep wires and tubes relatively unobtrusive it's basically got a white background.
The lights are not on in any of the pics.