Not everyone is blessed with "hard" and/or alkaline tap water. Recognizing this, several manufacturers, including SeaChem and Kent, have developed buffering salts in an effort to simulate rift lake water parameters. These serve to harden the water as well as provide "critical" trace elements. These commercial buffers and salts can get quite expensive if you have a large tank, or multiple tanks for that matter.
Instead of investing in these, there is a popular home remedy that works just as well. All the ingredients can be acquired at your local grocery store: Epsom salt, Salt, Baking Soda. Common bicarbonate of soda is effective at raising the pH, not to mention itís very inexpensive. Epsom salts (i.e., magnesium sulfate) can be used to harden the water, raising the GH. And then you could also add salt to increase the general hardness of your water. I recommend using non-iodized table salt; however, others use Potassium Chloride or even Instant Ocean®. You can read more about the differences between these salts in my article on Aquarium Salts. For a few dollars, you can mix up enough Rift Lake Buffer to last you a year or more.