If you've ever collect plants from the wild, you'll find most of the time they are growing in a very fine muddy substrate with high amounts of rotting organics, (dead leaves etc.), with next to no oxygen around the roots.
I've collected in Venzeula, Brazil, Bolivia, Guinea, Senegal, Mali, Zimbabwe, Zambia, Rwanda, Zaire, Vietnam, Laos, Cambodia, Thailand and never found them to be growing in claen aerated gravel. Nearest to it was a weird plant I found in the Canaima national park in Southern Venzeula which had almost no other orgranic matter.
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Have you ever seen the plants sold in LFshops planted in soil, nope, they,re in gravel. Food for thought.
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Most LFS's use undergravel filtrs in their tanks requiring the use of gravel.
I use swimming pool filter sand - doesn't compact so much.