If you keep snails: Common aquarium snails (sometimes referred to as “pest snails”) can be a benefit to your aquarium's gravel bed. Two of the three common types of snails found in aquariums — Physa and Trumpet snails – are known to burrow into the gravel, with trumpet snails being particularly enthusiastic burrowers.
My best consultant Guru Google seems to say gravel is fine per the quote above. Your substate looks like the large gravel I get from Pet Supplies Plus.
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