Suddenly unable to get zero reading

So was on here a few weeks back and not had any issues until now. This is the second time of using our RO plus DI vessel system 

For some reason we can't get any lower than 10 TDS 

Filtered then checked before DI resin stage and its at 20 TDS then after this stage its only getting as low as 10 TDS 

Why could this be happening? 

Any help would be really appreciated 

Poor quality or depleted resin, not enough resin in the vessel.

Thank you Martyn excuse us we are beginners but how do we know if its poor quality or not enough? 

Enough is about four inches down from the neck of the vessel, poor quality i guess you only know if it doesn't work. What make is the resin and where did you get it from? A known supplier or off the bay?

It was the resin supplied when I bought vessel so streamline I assume 

Will check the amount in there thank you 

Loops81 said:

It was the resin supplied when I bought vessel so streamline I assume 

Will check the amount in there thank you 

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I presume it’s a 10 inch which will explain your TDS

We've just changed the resin to a different one we bought and it's worked, thanks so much ???

Loops81 said:

We've just changed the resin to a different one we bought and it's worked, thanks so much ???

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Its worked for now but it hasn't solved your problem. Sorry.

Having 20ppm after r/o is high. Your resin won't last long I'm afraid. So we need to dig a bit deeper.

@doug atkinsonasked if its a small 10" di vessel. What size di vessel have you got? What r/o have you got? Where did you buy it? What is your tap water tds? What is your waste to pure ratio when processing water? What is your tap water pressure?

We ask these questions because an r/o not working efficiently will chew through resin. 25 liters on resin is around £90. Ideally a new r/o with quality membranes should be removing between 97% and 98% of the dissolved solids in your water.

Just as an example of efficiency. My first r/o was a 275gpd upgraded to a 450gpd unit. Our tap water was 254ppm. Our water pressure was 50psi and the tds of the water after r/o was 4ppm. That's over 98% efficient. Waste to pure ratio when processing water was 3 waste to 1 pure.