Is my TDS meter working?

[Magickiwi]

I bought this product from reefsupplies.ca http://www.reefsupplies.ca/online-st...ectrapure.html and it seems to be doing a pretty fair job of filtering water etc. It comes out odorless and tasteless. Testing for phosphate shows zero (my Hanna shows very tiny precense but the meter is extremely unreliable I find).

My perception is though that the TDS meter on the unit isn't working correctly. It displays zero TDS on the output but it also shows zero TDS on the input side of things. I'm dubious about if that is a reliable reading though. Most information I've seen estimates Calgary tap water as 160-600 TDS; including the city's own website. Is it measuring TDS AFTER the RO filter? Is that actually feasible to be zero TDS after an RO filter?

The Spectrapure instructions are extremely thin and they don't actually get into the nity-grity of how the unit works, what to look for etc. For example they don't say squat about the DI media. Is it color changing? What's the lifespan for it? Does an increase in the output TDS reading indicate it's time to change resins?