I would presume you are filtering in the following order:

Carbon - Chelate (Hybrid Cation) - Cation - Anion.

If so, and just for the record:

Carbon strips out organics - Check and maintain the COD level at something <
150mg/ltr
Chelate scavenges heavy metals - check lead content and replace/re-generate
when level exceeds drinking water level.

At this point you effectively have potable water (NaCl + H2O) then:

Cation - Hydrogen source captures Na and produces very weak HCl
Anion - Sodium Hydroxide exchanges Cl and leaves H2O, pure water for return to
final rinse.

Monitor levels in microsiemens or megohms as you prefer.

The problem you have described would suggest:

A       Maybe the Chelate is fully spent?
B       Maybe you use a rosin process rather than OA? This would demand a saponifier
in the wash rather than using pure water alone.
If this is the case, then you have almost certainly, a transfer of highly
alkaline (> 10pH) in the rinse which is killing your filters in minutes.

You MUST have an extended wet isolation between wash and rinse to minimise the
risk of transfer between wash and rinse. If you have not got this, you will be
replacing your filters every few hours!

Let me know.

Graham Naisbitt
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-----Original Message-----
From:   TechNet Mail Forum  On Behalf Of [log in to unmask]
Sent:   Wednesday, September 10, 1997 12:15 AM
To:     [log in to unmask]
Subject:        [TECHNET] DI water system

I am currently having trouble with our DI system.  I have changed the carbon
and replaced the resin in the anion column.  I also regenerated the cation
column.  The trouble I have is that the microsiemens (microhms) reading will
stay below 20 for only a few minutes and then it shoots off the meter.  Any
comments or suggestions would be greatly appreciated.

Thank you,

Mark Wilkins