Yeah I thought something is wrong, but doing more digging around it is normal. Rocks will leach minerals, no matter what they are. Dead, live, doesnt matter. Apparently only time 0 TDS is important is on initial tank setup, water changes water and top up water.
I wouldnt have never guessed that had I not taken this reading today and almost got heart attack haha
Interesting read on post 21 and 23 here about this topic:
http://www.reefcentral.com/forums/sh....php?t=2201617