I don't think that answer is quite as black and white as some of your other questions have been grimmy. On the one hand, convicts come from Lake Atitlan and Lake Amatitlan in South America, both with pH's around neutral. However, convicts are pretty adaptable, and most are captive bred these days. In the U.S., they are bred in the hard, alkaline waters of Florida. In short, I think they would be ok with a higher pH that would be caused by the crushed coral sand.
However, the bigger question is, is there something wrong with your tap water, grimmy? Does it have really low buffering? Unless your tap water has some problem with it, going out of your way to used crushed coral doesn't seem like it would be necessary.