RBU1, my recommendation for new hobbyists is to use an accurate test kit to determine the rate of dosing calcium (or any other element, for that matter, whenever possible) required to maintain the concentration between 420-475 ppm, rather than adding it indescriminately. I imagine that some members will disagree with my recommendation for the range, but it's always worked for me. You can certainly have too much calcium in a marine aquarium, but the question of "how much is too much" depends on what result of excess we're addressing (i.e. alkalinity decreasing as a result of too much calcium, etc.) and the concentrations of a few ions in the water, such as magnesium and sulfate. The addition of Liquid Reactor or any other product containing calcium, for that matter, will certainly benefit the coralline algae, so long as they have the required light and the water parameters are in check.