I want snails and have added several to my tank of guppies,. etc...They are not doing well. Their shells are flaking and getting holes. I researched enough to know the calicum level needed to be higher and put a cuttle bone in the bottom of my tank held down by tank decorations, but the snails after 4 days, have not paid any attention to this cuttle bone. What should I be doing to help these snails, but not interfere with my fish?

What kind of snails?

There are several things actually. Water quality will be an issue. Any signs of NH3 will severely harm a snail (with the exception to pond snails which have a higher tolerance).

Do you pre-treat your water with any conditioners like Prime to remove heavy metals? Copper is a no-no for snails.

You already mentioned the cuttle bone which is a start. Look at calcium rich foods and veggies as well. Ken's Fish makes a veggie stick that includes calcium. Another option is snail jell-o. There are several different recipes for this roaming around. One other that I have not tried is plaster of paris. I know people have used it but I have not so I can not comment on it.

Start with this and we can go from there.

Have you done any water testing? What is your ammonia, ph like that? These are important things to know for your fish as well. Snails are like the canary in the coal mine. You'd think they'd be tougher than the fish but they're really not, they're very sensitive to water quality. Calcium in the water acts as a buffer to keep the water chemistry from making sudden shifts in ph which can stress and even harm your fish, but they will cause damage to your snails shells before you notice any damage to your fish. If you ever notice your snails staying in their shells and not coming out it is a sure sign that something in your water is out of whack, and they'll warn you this way before your fish are damaged. I wish more fish keepers kept snails for this reason.

I'm guessing you might have pomacea bridgesii - those big snails the size of a nickle to the size of a quarter, often with tan shells and colorful bodies? If so, try feeding them some canned spinach, not too much, just a small spoonful. Your livebearing fish will enjoy the spinach too, and it will keep their digestive systems in good shape, but the snails will like it a lot. Eventually when your snails are feeling better they'll start nibbling on the cuttlebone. They may even be doing it now, just after dark.

(I know it has been awhile since you posted this, I hope everything has turned out alright)