Hi, H20ENG, my O3 sniffing friend... lol
You are right about that, the same thing happen in the mediteranium sea with caulerpa algea.:beer:
The snails, the seawater, the ermit crabs, and many other things that came as hitchhikers (fitoplankton and zooplancton and others larvae) came from the same place, the propabilities of a disease or parasites infectation is minimal, matter afect i'm more insecure of live stock/water diseases from the local shop then from the natural ecossistem, until this day, in thousands of marine/reef tanks no one had any problem about parasites or deseases.
Using natural seawater it' a normal and natural thing were i live for many, many years, almost everyone use it with great benefits, it's near, free... and it's the real thing.
Some people change 10% to 20% of tank water every weekend, saving money on mineral suplements, you can call it Live Water in comparation to artificial sea salt...lol, it's amazing to see the corals polips wide open betewen a water change... amazing!
Best Regards
Vitor Pestana