There are studies being done and have been done on calcium levels of ~500 ppm or higher and it just makes the corals grow faster. I'm sure there is some level where there will be an issue.
Mike
Many things can cause animals to go into spawning although it may have nothing to do with stress. A good example are SA Chiclids. Don't change their water for a few months and then do a large water change and POOF spawning. It was the old water, which had a high hardness, which was is inhibiting them from spawning. I cold also get feather duster to spawn at my command. All I had to do was take a stick and stir the gravel around them causing an increase in turbidity, which my be simulating a seasonal change , thus lets spawn
