Question on Ro/DI Water & Salt

[HowardW]

I just tested a 5 gal. jug of RO/DI water that I got from a new LFS and it came up at 290 TDS! I checked a jug of distilled water just to make sure the meter was correct and the distilled showed 0 TDS, then I also checked my tap water which came up at 265.

Now the guy at the LFS told me his RO/DI water may have trace amounts of salt because he used that big vat to make saltwater previously, but it would just be a trace amount if anything.

I also tested this water on my refractometer to see if it would give any salinity reading and it came up as 0.

My question is.......if there were in fact just trace amounts of salt in that water, would that show up on my TDS meter at 290, and should that also show up on my refractometer, or is 290 PPM too little to give any salinity reading?

I also noticed that when I used this water to mix up a batch of saltwater, it came out really cloudy??

Geez, I hope this guy didn't sell me tap water or whatever.

 

[Randy Holmes-Farley]

Yes, a trace of salt would shdow up as quite a bit of TDS, and wouldn't be a concern. Of course, he may also just be peddling tap water.


290 ppm TDS is too low to show up on a refractometer.

 

[HowardW]

Well I tried a couple more experiments to try and determine what the guy at the new LFS actually sold me......

I also tested the PH of this "RO/DI" water and it came up at 8.3 which would seem impossible because I don't think a trace amount of salt (290 PPM) would have the capacity to bring RO/DI water up to that high PH.

For comparison, I then took a 1/2 cup of my own distilled water and added just enough Seachem Reef salt to bring the PPM's up to about 290-300 on the TDS meter to match the TDS reading of the other water and then checked the PH and it was still way below 7.0 which is what I expected. I also checked the salinity of the distilled water with the trace amount of salt and it did give a very slight reading on my refractometer of about 1.001, but it may have just been variance of the refractometer.

And I still don't understand why this "RO/DI" water made my saltwater batch mix up all cloudy?

I think this guy may have sold me RO/DI waste water or something.....I dunno, but I'm going to call him today and ask a few questions.

 

[Randy Holmes-Farley]

Actually, my RO/DI water always reads substantially above pH 8.0 (usually 9+) even with nothing added.

The water shouldn't have made the batch cloudy. Maybe it is cloudy for other reasons?

 

[HowardW]

Ahhh ok, maybe I was thinking of my distilled water that has a low PH, as I've never tested the PH on other RO/DI water I've purchased.

I still can't figure out the cloudy issue though, I mixed it up the same way as usual using salt from the same bucket.

I sure wish I knew what's in this water and if it really is just trace amounts of salt

 

[Randy Holmes-Farley]

Many people do have pH 6-7 for RO/DI water, but it does sometimes run high, and such measurements are prone to big errors due to low salt content and low buffering. Not sure why mine runs high, exactly.

 

[Atomahawk]

Howard I did a quick test for you, it was easy as I tend to use the same buckets for mixing my saltwater and RO/DI water in.

Today:

My tap water here in my area is running at a pH of 8.0 at 60.1 F and has a TDS of 260.

My RO/DI is pH of 7.0 to 7.02 at 64.7 F and TDS of 0 to 1

Now when I use my buckets that I use to mix salt in the pH is still at 7.0 to 7.02 at 66 F but now the TDS is at 420. And I cannot read anything on my refractor. I would tend to believe the store as his explanation makes sense and I tried it.

Also, I can't explain why but when I mix up a fresh batch of saltwater in regular tap water not RO/DI my mix clears up faster than when I use the RO/DI water. And this no matter what salt I use IO, Seachem, Red Red Sea or Kent. I can't explain it I just see it. It's been a while since I did that , it's certainly the case in my area.

 

[HowardW]

Ok thank you Atomahawk!

The guy at the LFS insists it was just a trace amount of salt in that water and nothing more, and that it was run through his Spectrapure RO/DI unit and also the exact same water he uses in his own tanks.

 

[Atomahawk]

If you really want to know the truth bring a small clean container to the store and ask him to fill it up with RO/DI and do the test right in front of him. If he's telling the truth he wont mind I'm sure. Since his explanation makes sense i kind of believe him , but then again I never seen the guy so who knows. He should be using a seperate holding tank for the RO/DI though. Who knows why people would buy the water, personally I wouldn't want to use that water if I was making wine, LOL.