Water softener and DI resin alone

I mainly clean using traditional methods, but use Unger n-lite DI vessel for conservatory roofs and few houses that traditional would take me too long. 

Using just DI resin doesn’t last long and to prolong its life I purchased water softener I was really impressed with as TDS output was reading 0 when I first started using! That before water went through DI unit. 

After TDS reading was raising on output of water softener it was time to rejuvenate it. I did everything as per instructions. After rejuvenation drained water from the softener vessel and flushed it few times to ensure no salt is in water. The TDS reading after rejuvenation was at first sky high- 800TDS, so drained and flushed few more times. Now TDS reading of input and output is almost identical. 

Why was the reading 0 or close to 0 when I first bought it and now is not? 

When I first used water softener I was very impressed and considered it low cost alternative to lengthy process of filtering through RO system with no water wasted, but now I’m more puzzled and confused then ever before. 

Can you please share your technical knowledge and experience. I would very much appreciate that. 

Thank you

Firstly I've reviewed the smaller Unger n-lite DI vessel and I feel it doesn't really deplete all the resin inside.

Having a Softener prior to DI Vessel is pointless as Sodium and Calcium are bot Cations. What happens is Calcium does and exchange with the resin bead with then releases the Sodium element into the water making it softer.

When the resin is exhausted then you do the exchange process of pouring salt solution through the resin. The Calcium element is released and exchange for Sodium from the salt solution. During this process everything needs to go down the drain as your ppm will be very high.

So your Cation in your mixed bed is doing the same work so in theory you will get no extra life from your mixed bed.

doug atkinson said:

Firstly I've reviewed the smaller Unger n-lite DI vessel and I feel it doesn't really deplete all the resin inside.

Having a Softener prior to DI Vessel is pointless as Sodium and Calcium are bot Cations. What happens is Calcium does and exchange with the resin bead with then releases the Sodium element into the water making it softer.

When the resin is exhausted then you do the exchange process of pouring salt solution through the resin. The Calcium element is released and exchange for Sodium from the salt solution. During this process everything needs to go down the drain as your ppm will be very high.

So your Cation in your mixed bed is doing the same work so in theory you will get no extra life from your mixed bed.

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Is all this rinsing and salt bathing a false economy compared to the waste water of a quality RO @doug atkinson?

Point taken and makes sense on DI resin, but why TDS output on water softener was 0 when I started using it and is not the case after rejuvenation?

Full regeneration of small softener unit waste only 7.5 l of water to rejuvenate + few liters to flush after rejuvenation. 

Magnesium and calcium exchanged to sodium during softening process eliminate white water spots. If TDS reading is due to sodium it shouldn’t cause any spotting. 

Some window cleaners use water softener in hard water areas with their RO systems to extend life of membrane as sodium is supposedly more gentle on the membrane.  

Green Pro Clean Ltd said:

Is all this rinsing and salt bathing a false economy compared to the waste water of a quality RO @doug atkinson?

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Having a water softener prior to R/O in a hard calcium area will prolong the life of the membrane and you will get better rejection rate.

The issue is the amount of water window cleaners use they would have to do a backflush on their softener every 3/4 days because of the size.

So what I advise customers is factor in the cost of salt etc.. against changing a membrane earlier.

Thank you Doug Atkinson for your inside knowledge. Much appreciated.