TDS readings?

Is it common for your RO/DI to read 0ppm when tested for TDS? and what is a min and max number your should read? A good number and a number where you should be changing your membranes?

 

Yes, 0 for new filters.
http://www.3reef.com/forums/filters-pumps-etc/when-change-ro-di-membranes-73842.html

 

RO/DI, yes, thats what we strive for.
As for min and max numbers it depends of a couple of things. You really want to trend or track your tap water TDS, RO only TDS and final RO/DI TDS all three. The RO membrane by itself should be removing about 98% of the tap water TDS before it gets to the DI. The DI should be 0 TDS or very close to it, I change DI resin when I first start seeing signs of anything other than 0 TDS on a consistent basis. You may see a small spike when you first start making water but it should drop to 0 or thereabouts, if not its time to change the DI resin.
The membrane is the workhorse and many people overlook it which can result in higher operating costs since they have to replace DI resins more often when it is not performing well. Keep track of the RO only TDS and when the membrane is no longer giving you the TDS it should, say 95-96% removal of the tap water TDS its time for a replacement. If you wait too long DI starts costing a fortune.