Quote Originally Posted by rfeiller
red lava seems to be softer and a lot more dusting. black lava i found to be more stable. however the central systems that i have used red lava for nitrification in, handled banks of aquariums, it was not a closed system. water changes to the tune of 50% every other day. there was not time for an accumulation of alkalis, nitrates.
I think the black lava is typically real pumice versus the red lava is manufactured usually. I could be wrong, but that has been my experience with it.