View Full Version : TDS Question

02/28/2009, 03:43 PM
I purchased and set up a 75gpd Premium RO/DI system from you guys about a year ago. I actually didn't set it up until about 9 months ago. My house is on a well and we have a softener. The unit is set up after the softener. My TDS out of the tap is somewhere around 560(yikes!). The RO/DI consistently measures around 16 and has since I set it up. Would another DI cartridge help? Do you think the difference between 0 and 16 is enough to justify an extra cartridge.

FYI I have probably only produced about 150 gallons from this unit as my tank is small and I don't do a lot of water changes.

Buckeye Hydro
03/01/2009, 05:39 AM
If your DI water measures 16 we know your DI resin needs to be replaced. Let me ask a couple of other questions:

1. What is your pressure?
2. What is the TDS of your RO water?

How are you measuring your tds?

From our FAQ's:
We read Total Dissolved Solids in parts per million, or "ppm." We often try to measure TDS down near 0 ppm. Because this TDS level is so low, we have to keep in mind the sensitivity of the meter used to measure it, and the technique used to measure the tds.

Nearly any contamination in the sample container will cause an erroneous TDS measurement. Some plastic containers are difficult to get absolutely clean, and although they appear clean, they are not. An easy standard approach is to use a drinking glass as a sample container - use one right out of the dishwasher. Obviously, keep your fingers away from the inside surface of the glass.

Calibrate your meter. Use a calibration fluid generally in the range of the tds measurements you'll be taking. Some meters require a specific tds calibration fluid (e.g., 800 ppm), regardless of the tds levels in your samples.

Be careful with how you take your samples. Let's say you intend to measure the TDS in your 1) DI water, 2) RO water, and 3) tap water. Start with the cleanest of the three - the DI water. After letting the system run for a sufficient period of time that you are sure the tds levels have stabilized (to assure you are not measuring tds creep water), rinse the sample container two or three times with the water you intend to sample, and then fill the sample container with sufficient DI water to take a reading.

Now on to the RO water. The water we are interested in here is the permeate – i.e., the water that has been purified by the RO membrane – not the waste water. Make sure you understand which is which before taking the sample. Most RODI systems other than Buckeye Systems are not plumbed to facilitate taking a sample of the permeate. If that is the case, you’ll need to unhook some tubing – likely where the tubing attaches to the “in” port on the DI housing in order to take this sample. This is inconvenient for many people, and we find that people never do it. They report only the tap water TDS and the DI water TDS. Contact Buckeye if you need guidance regarding installing a couple of extra fittings and tubing to facilitate measuring the TDS of the RO water (permeate). When you take the sample, follow the same procedure described above – use a clean sample container, assure you are not measuring TDS creep water, rinse with the permeate several times before taking the sample, and use a calibrated meter.

Use the same approach to collect and measure your tap water as well.

03/02/2009, 07:39 AM
Source water is 499 ppm. RO is 28 ppm. DI is 13 ppm. Pressure is 30 psi. Temp is about 70 F. TDS measurements are taken with HM digital meter that I got from you with the RO unit.

TDS meter says to calibrate with NaCL. What does that mean to me?

As I said, the output TDS has always measured about the same. I have never seen a 0, that's for sure. I always use a brand new plastic cup and I drip water out of the output line directly into the cup.

About how much water should be made before a typical DI resin is exhausted given the incoming TDS of my water? Like I said, I haven't made much water compared to what a lot of other people do. I have 30 gallon garbage can as my reservoir and it's maybe been filled 5 times total. So on the pessimistic side I would say that I've made maybe 200 gallons total. Should my DI be exhausted already? Does it change color when it is exhausted?

Buckeye Hydro
03/02/2009, 05:33 PM
Your RO membrane performance would improve considerably with more pressure. I'm surprised you are getting any RO water out of the system to speak of. 40 psi is really the minimum most people are able to put up with, and with a booster pump you can get that up to 90 psi.

Are you on a well?

Yes - you should be seeing a color change on the resin.

Given the very high tds of your RO water, you should get 200 or so gallons from your DI cartridge, but that could be reduced based upon other water quality issues you may have.

You can use the calibration fluids we have on the website.

The primary issue I see with your system is the pressure - need to get that addressed and then we can troubleshoot other issues if they don't solve themselves.