This substrate is typically used for freshwater planted tanks, certainly should NOT be used in a reef tank
imho. From some research on the web "red flint" used to be the "rage" for growing plants in freshwater tanks. Anything that grows "planted tanks" well, is going to be real bad, as a substrate in your reef tank. It likely contains super high levels of
phosphates and other plant friendly minerals and chemicals. I could not find a break down of what some available red-flint contained but it just doesn't sound good!
Go with argonite, Old Castle white play sand (if you can find it), even "live sand" --- anything but red-flint !
Warm Regards,
