Most people use RO/DI here, not great water to use straight, especially for SPS.
There's not enough calcium or magnesium in tapwater to matter. In order to keep what's there you also keep a LOT of other stuff that you might not want. Check your local water source too, to see if you have chlorine or chloramines in your water. Most places around Houston have moved to chloramines, that takes carbon specific to chloramines to remove it. A tapwater filter is not nearly good enough for saltwater aquariums. Starting out with RO/DI water just helps in the long run, using tapwater to start the tank out even if you move to RO/DI when you go toward the harder corals to keep, you'll have a lot more initial algae/cyano/diatom problems with nutrients/silicates in the tapwater.