Watermaker - high TDS with new filters

[markcouz]

Some background...

I have a Seawater Pro system with dual membranes that has served me well since installation in Cape Town around May 2022. The system was purchased in July 2019 and stored prior to refitting the yacht for crossing to the Caribbean towards the end of 2022. At time of installing the RO membranes were dry with a powdery residue in the plastic sleeves, I blamed myself for poor storeage and expected the membranes to perform poorly - but after installing the TDS was around 120 and all looked good.

I ran the system in Cape Town (Simons Town) between installation in May and departure in Sept, with the TDS slowly clinbing to around 220, which was no cause for alarm as far as I was concerned. During the 3 month crossing with regular use the TDS continued to climb. By the time I arrived in Grenada in December 2022 the TDS was around 350. I attributed the increase to higher salinity water and higher water temps - again not alarmed.

Over the last 9 months the TDS has continued to climb to the point where it takes a few minutes to drop below 500 where I feel comfortable to switch from Test to Tank, during the 2 hours that it takes to top up it settles around 440.

Time to change filters...

I ordered 2 new SW30-2540 filters and installed them yesterday. After installing I ran the system for an hour to flush the new filters with the lowest TDS towards the end of the hour being about 350. Today I ran the system to top up tanks, and after an hour the TDS was 440! Exactly the same as the filters that I just changed!

My question - is there any other source of contamination possible other than dodgy filters, for instance is it possible for failed O-rings to allow some bypass to contaminate the product and give a high TDS?

Note that TDS readings are taken from the built in tester, and occasionally confirmed with separate hand held - so I dont think it is a dodgy TDS meter issue.

Thanks for reading.