RO water

Can I test the RO water I get from the LFS for Ammonia, Nitrite, Nitrate, PH, Calcium, Phosphates, Magneisium and KH like I would test my aquarium water before I add salt just to see if I am buying good water or do I need to mix salt with it first?

 

get a tds meter and bring it with you. I really don't think the tests are meant for fresh water, so I'm not sure if you will even find those thing you mention in fresh water......hmmmmm

a TDS(total dissolved solids) will tell you if their water is good or not. They should even have one.
TDS CONDUCTIVITY TESTER HYDROPONICS METER 0-1999 PPm - eBay (item 250282288466 end time Aug-20-08 07:37:06 PDT)

they go cheaper and they go way higher, but I'm pretty sure they all work the same.

 

a different indicator is used for testing freshwater pH. Usually KH, Ammonia, and nitrite indicators can be used for marine and freshwater. I am not completely sure about the others.

 

You should be able to all of those with an appropriate kit though calcium, magnesium and KH will likely all go up quite a bit once you add your salt so I'm not sure that you gain anthing by testing for them. Your fastest/easiest test would be to get ahold of TDS meter. RO/DI water should have TDS reading of zero (or at least a lot closer to zero than you have at home). If you're getting water with negligible TDS and no phosphate or nitrogen cycle compounds, you should be good.