Thanks for asking:
I'll try to make this short and to the point of concern.
The dry base your inquiring about is not treated prior to shipment. Although, mostly quarried on land as a terrestrial base, some are procured by raking the shoreline along rugged outcroppings. So to answer your question, yes, some rocks are collected at or just below the innertidal zone, and then shipped to a holding area. The state of Hawaii uses this calcium carbonate limestone in construction of their major roads and highways inside the state. Concrete is just too expensive to ship to Hawaii. Most of the base rock has been sitting landlocked for many years. Weathering due to nature helps in eroding such undesirables that may hitchhike itself upon the rocks. Although, dust from transport via ocean containers seems to be the biggest of all concerns. Sand and dried plant life is non-existent or present.
If you have been to Hawaii, you will notice that the waters surrounding the islands are pristine. They're nothing like the beaches and coasts belonging to the continental US. Strong ocean currents pull water away from the islands in a right to left motion. This current is known as the North Equatorial Current. A relatively slow eastward flowing current picks up steam when approaching the islands. The islands are populated by vigorous eddies or swirls, which obliterate the slower average circulation of the N.E. current. This helps in eliminating pollutants and debris from inward lying waters. Strong state regulations and measures concerning water quality insure that pollutants entering the harbors and seagoing waterways are at a minimum.
I tested this base rock many moons ago in a trial experiment before we decided to go with this endeavor. With the ban on Florida limestone, I knew that an alternative was needed for a starving group of aquarium enthusists and
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reefers. I found that the water & PH in my system was stable and no ill effects arised from the use of this type of base. PH = 7.8, SI = 0, Cu = 0, P04's = 0, Fe = 0, MG = 0. Fish introduced after cycling showed no ill effects. Coralline algae flourished and corals were not affected. I use this rock presently on all my accounts and in all my aquascape creations, so far to date, everyone I have contacted approves of the look, quality and diversity of the base rock we offer. However, don't take my word for it, you can check our feedback on ---- if in doubt.
http://cgi2.----.com/aw-cgi/eBayISAP...userid=hirocks
HTH :santa: