I like freyar's suggestion. As for the ongoing damage vs. resist energy, I see that as rewarding prepared parties a bit. Also, it'll take a chunk out of any protection from energy spells that are up instead.
Well 6d10 plus 3d10 over 3 rounds still seems a bit high. Not only is that a total of 15d10 damage (an average of 82 damage), it means its breath weapon is likely to recharge while its acid is still ongoing.
Maybe drop the rounds of ongoing damage to one or two?
One round ongoing acid breath is fine by me, it's looking dang near finished.
I do have one question. Why does its acid not affect stone? Its description says it eats minerals and creatures from the elemental plane of Earth, surely it stomach acids can digest them!
I was also wondering whether it could have the Earth or Extraplanar subtypes since it eats Earth creatures. A glitterworm's not an Outsider or Elemental though, so I'd deduce it's unlikely.