Thanks Todd.
We got in touch with Calico Jacks via their Facebook page. This not being high season, they replied to give them a call the day before. I'll be heading south down the reef as you suggested.

I got a reply from an email to the Rhodes Beach Resort in Samuel's Bay National Marine Park. There is a $10 daily charge to use their facilities. We'll snorkel the coral reef at Samuels Bay and also check out the infinity-style Oceanside Pool.