Did I get the wrong di

[bjc451]

I have a 4 stage spectrapure and replaced with brs pro mixed bed resin. Last time mine was blue and this time it is purple

 

[Shirak]

Purple indicates it's the Cation that is colored. Usually the Anion is the one that runs out sooner so you may find your TDS meter indicates the DI cartridge is shot before all the purple beads have changed color.

I think most people that are using a single mixed bed DI cartridge would use the one they call Bulk DI Resin (color changing) That has the blue anion beads instead of the purple cation beads.

You can still use the one you have but need to monitor the output tds which you should be doing already anyway since the blue mixed beds will start to allow stuff through before they fully turn color too.

 

[bjc451]

So it won’t technically last longer because one will get used faster before the other is fully exhausted

 

[Shirak]

So it won’t technically last longer because one will get used faster before the other is fully exhausted

Correct. Which is the same case with the blue mixed bed but it looks like it's all exhausted when it's time to change it because the anion usually runs out first. The cation is probably still good but you just don't see it since it isn't colored. This is done more for those that don't monitor actual TDS and just change it based on resin color. Or to at least warn you when it's getting time to keep an eye on the TDS and be ready for a new cartridge.

With the purple mixed bed used in a single DI cartridge setup, it will most likely appear that there is a lot of life left even when the anion is exhausted because you will only see the color change on the cation (purple) beads.

 

[Shirak]

So in case you are wondering.. why make the mixed bed with purple cation? Some people use 2 or 3 DI cartridges with all anion, cation and mixed bed, hence the need to perhaps use a mixed bed with cation indicator beads.