Only the goals of your project can best answer the question. In absence of goals, just arrange your Reef Balls in a pattern similar to your observations of the natural reefs in the area. Dr. Bill Lindberg is studying deployment patterns now and can probably assist if your goals include the recruitment of specific fish species. Generally however, fishing reefs are better spread out and diving reefs need to be tightly deployed. A combination of the two makes an excellent reef.
Regular concrete has a high pH when it is first cast.
This is caused by excess calcium hydroxide in the concrete. Eventually, the pH of the concrete in the sea will approach the pH of the sea which is about 8.3. Some types, like barnacles, are resistant to the pH difference so the growth that occurs on concrete that is not pH neutralized will favor those species. By the time the pH is normal, the resistant species have settled and set up defenses to repel settlement of other marine life forms to the reef. We recommend that if microsilica is not available that you let your concrete cure in the rain or a freshwater pond for about 3-6 months before deployment.