Help understanding water paramters

[reefo420]

So my tanks water quality hasn't been the best so I've decided to test the water I'm buying from the LFS,
checked the RO water they have been giving me with an apera tds pen and it's showing 170-190 ppm, the pen is calibrated
i've tried my own ro water system that i've just got and tested it with the same pen and it's showing 1ppm
should i change most of the water? why would something like this happen

 

[RocketEngineer]

Yes, I would do a big water change with the better water if possible. Consider adding a Deionizing filter as a final stage.

It happens because the RO membranes range in removal from 98% to 99.5%+ depending on input water quality, water pressure, temperature, and probably a bunch of other small factors. Some areas have better source water than others.

 

[PatW]

If their RO water is 170 tds, I wonder if they are even running it through an RO membrane or have one that is still effective. My water comes through my RO membrane at 2 tds and after DI 0 tds.

You might give the notion of getting an RODI system serious thought.

 

[Floyd-]

This is why I make my own RODI and salt mix. If you do buy from a local shop id check it every time you buy it just to be safe.