Hello; back a few decades I was often breaking down a tank. I have gravel in containers from the 1970's. I will siphon out the gravel into a five gallon bucket then store it. When needed I give it a good cleaning by rinsing. I recall one time rinsing gravel which had been in a bucket for many months. As I scooped out the quart sized portions to rinse I noticed some MTS still alive. The gravel had stayed damp by having a lid on it. They are tough.I have MTS snails and I have tried puffers, loaches, crabs, crayfish, assassin snails and nothing eats those. I even used bleach and hydrogen peroxide and they always come back.