What should my tds level be?

[havefun]

My RO unit arrived today and since I can't fill my tank (story in another post) I've been playing with the unit (getting it mounted on the wall etc).
I used the tds meter on just my plain tap water and it was around 375. Then, after letting the RO unit run for 15 minutes I tested it and it was 9. I know if I also had a DI unit the reading would probably be 0, but is 9 typical for just RO?

[fishfreek]

the TDS meter is not an inline unit I take it since you tested your tap water with it. When you test your TDS make sure the vessle your using to hold the test water is absolutly clean. Just a few dust particles can screw up your TDS measurements. Also make sure you use seperate vessles for tap and RO water testing or you wipe and dry the vessle upside down before testing the RO. The reason is that RO is so close to pure H20 that even the most minute contaminates can give a false TDS measurement.

I would be willing to bet if you measured your RO a half dozen times over the corse of an hour you might end up with 4 different readings all within 3-5 points of eachother. At the low level your testing that can be a fairly significant percentage of error but at the dirty tap water side a 3-5 diffierance is insignificant.

I would say acceptable RO TDS measurements would be 10 or under. Yes adding an DI stage should bring taht down to 0-3.

With a TDS of 375 going in and 9 coming out without a DI stage, that's quite good. I've seen some RO filters only able to keep it under 50. I'd say that's about as good as your going to get unless you add the DI.

With such a high TDS, you'll need to keep a close eye on your prefilters, they will exhaust quickly.

Cheers
Steve

[captivereefs]

9 is great especiallay since it was 375 going in!