Ways to add calcium to your tank?

http://badmanstropicalfish.com/articles/article82.html
"... The water should have a GH and KH at least of 4 degree (bit more than 70ppm) for each. Ideal hardness and alkalinity would be above 6 degrees (>100ppm) for each KH and GH... "

Pet store bird supplies.
cuttlebone will dissolve slowly enough that you will probably not notice a change in pH.

Flavored cuttlebone might have harmful additives though...make sure you get plain one (usually cheapest).

Cuttlebone can be placed inside canister or hob filter along with media or pushed under substrate.

jrafael helped me out with info last year.

pH lowered by the the injection of CO2 isn't exactly the same as that produced by a lower KH value.
HTH

I bred crap loads of brigs and apple snails years ago to sell around the state since you couldn't transport apples across state lines anymore and nobody had pink or purple brigs (got $5 apiece for dime sized babies at all the LFSs and like 50 cents a piece for apples at quarter size).
Having hard water and adding the calcium essentially just buffers the water but doesn't actually get absorbed by the snails.
You have to feed them lots of calcium rich foods to keep them from getting growth lines at the edge of their shells.
Dandelion leaves, collard greens, and spinach are good choices (descending order of calcium content). I fed blanched dandelion leaves in the summer when I could just pick them outside and collard greens in the winter from the store.
You can also give them Tums. They love the fruity flavors and they will chew on them and vacuum them up as they dissolve. Don't use calcium supplements that have vitamin D.
I also made plaster of paris food blocks which the snails and plecos both love.
Just get some DAP Plaster of Paris (the cheap stuff) and mix it with enough water to make a thick paste (really thick--you shouldn't be able to pour it). Add some spirulina powder if available until it is just the palest green (too much and the blocks fall apart) and granulated fish food (cheap crap works fine).
Scoop the mixture into the little plastic sauce/dressing cups you see at restaurants and let them harden for a week.
They last for a months depending on how much the snails and fish chew on them and they wont cloud your water or dissolve if you didn't use too much water when you mixed them.