substratum
Shohin
Thank you. I'm in 8b, so my experience wouldn't be materially different with respect to freezing.It does not go soft for me. But as coh points out, I am in a warm climate (freaking hot right now actually!) where we don't get much freeze-thaw. And I repot fairly often, usually no longer than every two years. As a side note, I use STS as a substrate ion my planted aquaria too, and it does not degrade in tanks that have been set up for years.