GuppyLove I've never tried the tums myself so I can't give you first hand knowledge there. Just a fact that I read somewhere. There was no mention of any ill side effects from using the tums. It was stated that from time to time the person even gave his snails a fruity flavored tums as a treat and they loved it. (I'll see if I can find the article)
If you're afraid to chance it then I would suggest a plain calcium tablet (for human consumption). I know some of our members have used them for their snails.
Ken
Edit: I can't locate the article at the moment. If you'll check out the link I provided it will give you several options for increasing the calcium.