TDS Meter Failure?

I recently purchased an entire rig from a friend of mine who was moving out of state. Along with it came a 6 stage RO/DI system. The first thing I did was replace all of the cartridges since I didn't know how old they were. I've got it fired up and it's running great.

Using API test kits, I can tell that the GH/KH are down coming out of the system. Previously, I couldn't measure either reliably because they are off the chart coming out of the tap. Now, they're both down around 4 degrees. Phosphates are also down to 0ppm. They're 10+ppm out of the tap.

The system also has a dual TDS meter attached to it, measuring input from the source and output from the DI. Given the various readings I mentioned above, I know the system is working. However, the TDS meter is displaying a similar output value as it is the input value. Both are typically within 2 or 3 ppm of each other and are normally around 250ppm. Do I just need to replace the TDS meter as well?

Thanks,
Jonathan

 

Did you flush your cartridges for at least a half hour? Another thing you might want to do is disconnect the lines at the tee's where the TDS probe are and look thru the tee to make sure the pins aren't parallel to the flow but perfectly crossflow. Also change the batteries couldn't hurt anything.

 

Yes, I flushed them for 2 or 3 hours after installing them.

The way the probes are installed now, if you were to draw a line between the electrodes, that line would be perfectly perpendicular to the water flow. Is that correct?

I haven't changed batteries yet. I'll do that.

Thanks,
Jonathan

 

Yes that is correct.

You might want to get a hand held TDS from Lowes or HomeDepot. It's a good idea to double check the ro/di in storage before using it and in this case will tell you how well the used one is working.

 

Typically a dual inline TDS meter on an RO/DI system reads the post RO membrane and final treated water (RO/DI) not the tap or source water so your readings will be low for the IN probe and should be 0 on the OUT probe. Its not much use to read the source water if you only have the one meter since what you need to know is how well the membrane is working and how well the DI is working. If both are reading 250 or so you may have a RO membrane problem. Did you change the membrane and DI resin too?

I do prefer to have a handheld meter also myself since it gives me portability and accuracy over the dedicated inline type which cannot be used portable since thye must have flow past the probe to function properly and are not as accurate since they are nt temperature compensated. The inlines are a great rough guide, kind of like a litmus paper test but the handhelds can be very accurate if you get a good one such as the HM Digital TDS-3, TDS-4 or COM-100.

For a quick test on the inline, remove the probes from the tees, rinse them well with some bottled distilled water since you are unsure of the condition of your unit at this point, then stick them in a clean cup of distilled water and check the readings. Thye should be somewhere close to 0 TDS. Although this is not real accurate it is a good troubleshooting tip. When you reinsert the probes in the tees, they have an indicator on them as to which way to orient them, basically if the words IN and OUT are facing forward they are correct.