First-time caller here, but I thought this would be a great place to post about a successful experiment with my aquarium.
I have envied the rock backgrounds Cory has been showing off lately, but had decided to just to paint the back of my tanks like normal. After rooting through the random leftover paint bin in the garage, I came across an old spray paint from my youngest daughter's old school project. Her project was to create a solar system out of styrofoam balls; mine became an experiment to see if it would look like as a backdrop in an aquarium.
Long story short, this "Stone Texture Finish" spray paint looks great! I applied it to the outside of the aquarium on the back, and it looks like a reasonable rock analog! Cheap way to add a rock look to your aquarium.
https://www.amazon.com/Krylon-K18201-Coarse-Texture-Granite/dp/B000BZX6VO/ref=sr_1_5?dchild=1&keywords=black%2Bspeckle%2Bpaint&qid=1600793761&sr=8-5&th=1