3lb Black Cactus Pea Gravel Rocks,1/4 Inch Pebbles for Indoor Plants, Natural Succulent Rock and River Rocks Decorative for Aquariums, Vases, Outdoor Gardening, Top Dressing for Potted Plants

Since the mobile app likes to wreck image posts, here's the caption in a comment form: TLDR: Glofish Aquarium Gravel Solid Black is the only substrate I've found so far that's actually black. Pictures in order: All 8 substrates wet (under water). Added a nice black velcro reference since the black plastic tray wasn't very black. All 8 substrates dry Substrates: Fluval Stratum (Amazon) - Not advertised as black, but I've had multiple people tell me it's black. Verdict: it's brown. A very dark brown, but it's brown. Black Lava Rock (Scenic Hill Farm Nursery Online) - Not advertised as an aquarium substrate, but if you ask for black substrate, this is about half the suggestions you'll get. Verdict: it's a mix, some black, but mostly varying shades of brown with some red and even white mixed in. I've had several brands of lava rock and they all look more or less the same. Caribsea Eco-complete (Chewy Online) - Fancy lava rock with some beneficial bacteria in it. Verdict: more uniform than most lava rock mixes, but still mostly browns with a tiny bit or red and white. Aqua Natural Bio Substrate (Amazon) - Another beneficial bacteria substrate, this one closer to a sand than a gravel. Verdict: Probably the darkest black substrate here, but with a lot of brown and red bits mixed in. Seachem Flourite Black Clay Gravel (Amazon) - Common suggestion for inert, black substrate. Verdict: it's gray. Yes, it's a lot more gray when it's dry, but it's still gray when wet. Aqua Natural Diamond Black (Amazon) - Marketed as a very black, shiny substrate, again closer to sand than gravel. Verdict: it's kind of a translucent green with some dark black bits mixed in. It actually looks pretty good from a distance, but close up it's very obviously not black. Glofish Aquarium Gravel Solid Black (Amazon) - Regular gravel that's painted black with an aquarium safe paint. Verdict: it's actually black Generic Black Pea Gravel (Amazon) - Just some plain black pea gravel marketed for decoration and soil dressing. Verdict: it's pretty gray and has bits of white and red mixed in. The winner is Glofish Aquarium Gravel Solid Black, it actually looks black under decent lighting. I'd still like to try Diamond Black Blasting Sand, although from pictures I've seen online it looks an awful lot like the Aqua Natural Diamond Black (coincidence?). I'd also like to try obsidian shard, but that's really expensive and I don't know if I care that much. Finally, if anyone knows of a good source of actually black lava rock lmk, I love the texture of lava rock and I'd really like to find a truly black lava rock substrate.