Originally Posted by Hoppy
Isn't it interesting that we believe that MTS, which is based on dirt or unknown composition, is "good", but, old substrate, which has miscellaneous organic stuff mixed in, leaving a substrate of unknown composition, is "bad". Personally, I think if I can stir up the substrate a bit and it stinks bad, it is "bad", but if it doesn't stink, it is "good".
hahaha! The debates and concerns will never end on this one.
I have a single tank that has the same substrate (without deep cleaning) >30yrs wet. I've added finer grain material in a layer to increase the depth a couple times once I added plants to my tanking but the original river gravel still sits on top of decades old and unused UG filter plates.
I use it as a breeding tank.