Testing for chlorine from an RO filter . . .

[Wookii]

I have been running my RO filter for around 15 months, and have yet to change any of the carbon block filters or membranes. I'm essentially running double the usual number of carbon block filters, as one is a general carbon filter, and the second is a chloramine filter (which also deals with chlorine). I have an inline TDS meter which is still registering the same 6ppm production water TDS that it was when it was first set-up.

I am aware I may need to change the carbon filters in due course, but I only want to do so when I absolutely need to. If I had followed the manufacturers instructions I'd have already changed the carbon filters twice and replaced the membranes already (and I suspect needlessly). Call me an old sceptic, but I am acutely aware it is in the manufacturers interest to have me replacing the filter cartridges as frequently as possible, where as I want to replace them as infrequently as possible for both cost and environmental reasons.

So my thinking is I should be able to test for any residual chlorine in the RO water produced. As long as it is zero, the carbon block filters shouldn't need replacing right? Likewise, I shouldn't have any concern over the membranes until I start seeing a rising TDS in the production water?

Catching the depletion of the carbon block filters early should also prevent any chlorine damage to the membranes extending their lives. So with that in mind, exactly what should I be testing for? Testing for Chlorine seems to be pretty common place for drinking water systems and swimming pools, but there appear to be tests for free chlorine, total chlorine, and chlorine dioxide. I'm going to have a guess that 'total chlorine' is the one I want, but can anyone confirm?

As always, if there are any holes in my thinking, please feel free to highlight them?

 

[Stu1407]

I had a similar situation in that the TDS of the tap water here is just over 100 so I would get a TDS of zero after the resin filter for six months or more. When it went up I just used to replace the resin filter and it was down to zero again. I agree with you on the manufacturers wanting to sell you the consumable bits, no doubt based on a worst case scenario for the contaminants in the water.
Like you say though testing for chlorine in the product water will give you an instant reading if any is present. In which case I would replace the two carbon filters to be safe and also maintain the life of the membrane.
I just use dechlorinated tap water now, which is bliss after years of brewing RO salt mixes.

 

[brhau]

Total chlorine should measure it, if you don’t care about the fraction of chloramine to free chlorine. If 0.2ppm chlorine is the only thing prompting you to change your media, you could get some more mileage out if it by using dechlorinator.