Also, I heard of a really cool way to buffer your pH and supplement calcium as well:
Go to a feed store or some sort of place that sells large amounts of crushed or otherwise mangled oyster shells; buy just one bag, depending on the size of your tank, and go from there.
Take a large pot (preffereably stainless steel), and put regualr tap in with the shells; boil for like an hour or something. What your doing is trying to get the left-over flesh and decaying organics out of the shells. Then take the shells and place in a large strainer, and rinse them like theres no tomorow. Then, just mix the stuff in with your sand! Every time your pH gets too acidic or low, the water automatically begins to corode and break down the oyster shells, balancing pH, and releasing calcium into the water.
I thought it was pretty cool... 8)
