How long does DI resin last before the TDS shows that it needs changing?


Imagine if you could keep your pure water TDS reading at zero for longer:


In this article I will show you the best way to optimise your DI resin so that it lasts longer between changes.


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But first let us answer the question - How long does it last?

In the best conditions it can last up to 4 weeks. It does depend on several factors including the quality of water entering the vessel, the temperature, the pressure and how compact the resin is.

It is also important to know the how to store mixed bed resin so that it doesn't go bad and how to use the resin to increase the lifespan.  but we can get onto that later.



Shows example of TDS meter reading for window cleaning water filtering
Example of TDS meter reading over one month


When To Change?

This is a very common question - Facts is, what ever anyone tells you about how long DI resin lasts or what ever on-line calculator you use, when your TDS meter reading creeps up to five or more then it is time to change the resin.


You will fine that the TDS meter reading doesn't increase steadily over the month.  It tends to go from zero to one after a couple of days then sit a one to three for about three weeks and then shoot up to five then 10 then fifteen over a couple of days as you can see from the graph.


When to change, according to TDS meter reading.

According to the graph above I would change it on the on the 26th of the example month, as soon as the TDS meter reading increases.

TDS meter shows that DI in vessel needs changing

Reading shows that Mixed bed resin needs changing Step by step instructions to Change mixed bed resin in DI for window cleaners.


Your DI resin may last longer if you follow these 10 steps when changing your the resin in your vessel.

Step 1 

Test the water as it leaves the Reverse osmosis filters, before it enters the DI tank.

Test the water as it leaves the RO filters
Test the water as it leaves the RO filters

If this reading is very high then the filters will need a flush or change before you move on the change the resin in the DI vessel.


Step 2

Open the tank and remove the cartridge.

Open the DI Vessel and Remove the Cartridge

Step 3 

Empty the Old Used Resin


      Dispose of Old resin

Step 4

Clean the Vessel with DI water not tap water.  Also Clean the Lid and sponge with deionised.


      Cleaning the vessel and lid with Pure water not Tap Water

Step 5

Next start to refill the vessel.  You should add about half a cup of mixed bed resin.


      Fill vessel with mixed bed resin

Step 6

Tap it on the ground about twenty times before adding another half cup.  This will compress the mixed bed resin and help to extend the life of the resin.


     Tap to compress the mixed bed resin


Step 7

As the vessel fills you can put the lid on and tap it on the ground to further compress the resin.  

    Add more resin to the vessel

Step 8 

Then remove the lid and fill more resin to the gaps left by the lid.

    Continue to change resin

Step 9

Some of the resin will be on the outside of the vessel, so once the lid is back on, clean the vessel with Pure water.


    Once full clean the vessel with pure water not tap water

Step 10

Re assemble but don't re-connect the pipe yet.  Run off the filtered water until it runs at its lowest possible Total dissolved solids.  This could take about five minutes.  Connect the pipe and run for another five minutes before testing.  If you are using a container to test the pure water, clean the container with previously made pure water to ensure that your TDS tester doesn't find particles left behind from previous tests.

Clean before testing

Clean Container Before testing the water

TDS now Zero

Zero TDS

How Long Does DI Resin Last For Window Cleaning FAQ's 

Q) What is the best way to store Mixed Bed Resin it increase its shelf life?

A)  It is always best to store the resin in a sealed container or bag.  This will stop the air getting to the resin shortening its shelf life.


Q)  What is the lifespan, once it is in the actual tank, not being stored?

A)  This will depend on how much water it is polishing and the quality of the water that enters the vessel.

As a guide water that enters the vessel at 12PPM and polishes 250 litres per day, 5 days per week should do about 5000 litres or a months window cleaning if you are using 250 litres per day.


Q)  Is it OK to handle the Resin with your hands?

A)  Resin can dry out your skin so you should avoid touching the resin if possible


Q) Are there any other health and Safety Issues when changing the resin?

A)  Yes - If the resin needs spill onto the floor they can be extremely slippy.  Make sure you sweep them up or better still put down a plastic bag that you can dispose of after the change. 


Q) If my tap water TDS is very low can I cut out the RO Step?

A)  It is unlikely that it will be low enough to plug in direct.  Even if it were only in the low 40's this could reduce the life of the DI by a week using my calculations 


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