well its been a while since ive been to kawhia, but last i can remember there was no rust at the beach, i havent added any sand or even gotten the tank yet so dont worry, im just asking questions,
one thing that puts me off is that it wouldnt act as a ph buffer
just so that you can see what i was thinking about have a look at the link here
http://www.advancedaquarist.com/issues/ ... uarium.htm
i still havent decided on the final dimensions of the new tank but it will be about 100litres with my 88l as the sump
thanks for the offer chimera, the argonite sand (white coarse stuff) is what i was planning on if the black sand didnt turn out to be suitable