I'm building a new (eventually discus) planted tank with Eco-Complete as the substrate. I was looking for some large black/grey pebbles to create tiers. Has anyone ever heard of, or used Mexican Beach Pebbles? I can get some for FREE, I've been told they're expensive so wooo! Just wondering if they'd have any impact on water chemisrty,I know about the "vinegar test", but was looking for some hands-on experience.

Cheers!