Inline TDS meter reading high

[Tastee]

Hi all, I have an Aquatic Life 4 stage RODI unit and use the supplied dual TDS meter. This appears to be a common unit and I also see it marketed as a HM Digital TDS Monitor, model DM-1. This has been setup for 3 years now and recently the probe connected to the RODI output is reading high. Prior to this it was reading 0 or occasionally 1, but now it bounces around all over the place between 25-55. I have checked with another, newer, TDS monitor I have (same brand) and it confirms that the output is actually 0, so it's not a problem with the filters, which are all still going strong. I also replaced the batteries in it in case that was causing the issue, but that didn't change anything. I have also tried soaking the probe prongs in Citric acid, and even giving them a light clean with sandpaper and a fine wire brush in case that fixed it. Initially after lightly sandpapering them it went back to 0, but a few weeks later it is back to showing 30-50.

The inlet probe is working fine, showing my incoming TDS is around 76, which is normal. I have my other TDS monitor connected before and after the RO membrane and it shows around 74 TDS going into the RO and 0-1 coming out. As I mentioned when I move my new probe and temporarily place it in the RODI outlet measuring point, it confirms TDS is 0.

Has anyone had any issues with these probes?
Any tips to clean them or otherwise address this issue?
Or is it going to need to be replaced?

Thanks in advance and happy reefing!

 

[Jekyl]

I would replace. Best to be sure

 

[Tastee]

I would replace. Best to be sure

Thanks. It looks like I can get one delivered from Amazon for about A$33 which is much better than other online prices I have seen locally (some close to A$100!), so I will grab another one. I would be interested however to hear if anyone else has had issues and any success dealing with them.