We usually say skip the crushed coral for that very reason. A simple aragonite sandbed will be fine. Some even use pool filter sand with success. But you don't disturb the sandbed in saltwater, you set it and forget it.
In terms of water, you want to use ro
water rather than tap. Nitrates/phosphates can easily get out of control from tap. Personally, my ro
has been down for almost 2 years and I have been using distilled water you can get at Walmart or other stores with success. Is there algae in my tank? Yes. Is it controllable? Yes.