I'm guessing the DI
resin is exhausted. Non rechargeable DI
resin units are what they call mixed bed resins. They have an anion (negative) resin and a cation (positive) resin. The basic idea is that the resin exchanges an OH- ion for any negative ion that goes through such as Cl
-, F- and a H+ for any positive ion such as Ca2+, Na
+, etc. If you run the water through one resin type first, it becomes acidic or alkaline depending on which resin it goes through first. It then runs through the other and becomes neutral as the remaining counter ions also get replaced.
The drawback to that is as the PH
increases or decreases, the ion exchange efficiency drops as it becomes more and more difficult to further increase or decrease the PH
. The advantage of separate resins is they can be recharged.
Mixed bed resins can purify water to a much higher degree as the PH
remains neutral since the H+ and OH- and created at the same time. But what is used to recharge one, discharges the other and they are therefore a one shot deal.
And since the H+ ions are held in place on the resin by an amine functionnal group, as that resin runs out, it starts giving off amines that smell fishy. The cation resin almost always runs out first.
We use huge ion exchange units at work and that smell is a dead giveaway.