I have a very stable tank and deep-ish sand bed of about 3 inches. I mostly leave it undisturbed and let snails turn it over. It acts as a great filter and keeps my nitrates down without water changes. I set this up about 2 years ago as a no-WC tank to see what I could do with it. I change the water about 4 times a year to mostly make the sand bed look pretty.
However, I have always had these little worm-like things poking up from the sandbed. They go down pretty deep into the sand bed and can't be vacuumed out. If you vacuum the sand around them, and expose the base, they meet up at something that looks like a jumbled up colony. They have never seemed to bother anything, they're just unsightly because they leave castings on the surface which is why I have to occasionally vac it.
However, I have always had these little worm-like things poking up from the sandbed. They go down pretty deep into the sand bed and can't be vacuumed out. If you vacuum the sand around them, and expose the base, they meet up at something that looks like a jumbled up colony. They have never seemed to bother anything, they're just unsightly because they leave castings on the surface which is why I have to occasionally vac it.
