I am looking for recommendations on what substrate to use for my new tank. I am having a custom acrylic 240 gallon (96Lx24Wx24H) made and will be housing a single 12" Piraya Piranha. I am thinking of maybe using a black background but really want a natural look overall. I can't afford those custom 3D backgrounds at this point, as I'm already spending $7000 on everything (tank, fish, filters, decorations, equipment etc) which is majorly above my budget. I am thinking of putting in a tree stump decoration from Universal Rocks (
https://www.universalrocks.com/fish/tree/stumps/ts-007) and some fake plants from Universal Rocks (
https://www.universalrocks.com/fish/artificial-plants/ap-006).
I dislike those gravel (larger pebble) substrates and am thinking I may go with a 3mm sand or something like that but I really don't know too much about substrate so I'm looking for your ideas and recommendations on which one to use. I have a Python hose that I will be using to clean the substrate. Do you guys think I should go a lighter color or would that be a bad idea for Piranhas? Should I go black or something? Is sand a safe substrate for acrylic? I can;t have a substrate that will scratch. Please share your ideas!