I work at a plastic injection molding facility. I can get my hands on some plastic pellets and I was curious if this would be ok for rays. I would cut down on debris in the filter and also I could run a powerhead over it without disturbing it too much. I could keep the substrate clean but yet light enough I believe a ray could burrow in it. The link below will show you what it looks like. I am going to use a natural color like a black or white or tan. All i have to do is make sure the specific gravity is over 1.0. Please let me know if you see any issues with this. I am planning on keeping a ray. I doubt anybody has used this but if you have please chime in. Thanks
https://www.google.com/search?q=raw...KEwjm967evLjJAhUBXh4KHUEsBfoQ_AUIBygC#imgrc=_
https://www.google.com/search?q=raw...KEwjm967evLjJAhUBXh4KHUEsBfoQ_AUIBygC#imgrc=_