Join Date: Nov 2007
Location: NYC & Long Island, NY
The only snail that will turn substrate without fail is MTS (Malaysian Trumpet Snails). They typically burrow into the substrate during the day and emerge at night. Keep in mind, tho, that they rarely burrow more than one inch deep, so anything deeper than that could still become anaerobic.
I've read varied accounts of spixis and/or nerites burrowing, but MTS are the way to go for substrate mixing in my experience.
You can probably get them in a local pet store for free or very cheap. I got like 8 for $1 from my local pet store, and those 8 quickly became 20 within two weeks. You could also get some from someone on this forum, I'm sure someone would be willing to send some out to you for the cost of shipping.