There are a few people with stingrays knowledgeable enough to talk about the substrate. Though not on often,
JK47 is one of them.
jim barry is another. Other than that, I turn a blank to anyone else.
Carib sea torpedo beach... hate substrate, always have but this is the only stuff i ever used for rays. Doesnt stick to their disc and is a heavier grain so its not kicked up into the water column or into pump intakes.