Chlorine & your RO Membrane

Woodyman · May 3, 2022

Got an interesting email from HACH today. While I know I have no plans to personally or professionally buy this equipment, I thought it would make a nice reminder and give some talking points for everyone.

HACH emailed me a new inline continuous chlorine meter that will detect down to 8ppb (yes ppb, not ppm, so 0.008ppm) for RO units. While the meter itself can be yours for the low low price of only $4,900 - $7,900+ the content posted with the meter is more valuable to the everyday reefer making RO/DI water.

So according to research a 10ppb (0.01ppm) increase in chlorine bleed through can reduce membrane life by up to 25%. I don't know how accurate their testing is, as I don't know the methods, and they are ultimately a manufacturer looking to sell meters/monitors.

Now even without the capability to detect into the ppb range, any noticeable shift in chlorine bleed through to your RO membrane should be adjusted as quickly as possible by replacing a carbon block in order to prolong the life of your RO membrane. Remember a properly maintained membrane should last you 3-5+ years depending on usage. Do yourself and your wallet a favor and monitor your chlorine bleed through. Not only will you save $, but you also save the trouble of opening up the RO housing, and swapping membranes.

Now if you want to read up or spend thousands on a continuous chlorine meter, the link is below for reference.

Ultra Low Range CL17sc Colorimetric Chlorine Analyser with Standpipe Installation Kit

www.hach.com

Malcontent · May 3, 2022

Yeah, I got that email too. I thought it was interesting what they said about RO membranes. I've been detecting 0.02 mg/L chlorine in my "waste" water but I think I was getting that even after putting in several new carbon blocks so who knows...

Also interesting is their new fluorescence method chlorine colorimeter which can also detect ppb levels of chlorine. Only $2,375 and each test costs about $3 so I probably won't be getting one anytime soon.

Chlorine tolerance seems to be around 1000 ppm hours.

I did wonder who was running so much chlorinated water through RO filters. Apparently, desalination plants use chlorine to control biofouling then dechlorinates it then chlorinates it again to become potable water.

Muffin87 · May 3, 2022

Woodyman said:
HACH emailed me a new inline continuous chlorine meter that will detect down to 8ppb (yes ppb, not ppm, so 0.008ppm) for RO units. While the meter itself can be yours for the low low price of only $4,900 - $7,900+ the content posted with the meter is more valuable to the everyday reefer making RO/DI water.

The HI761 Hanna Chlorine Ultra Low Range Checker is $59 and reads between 0 to 500 ppb with an accuracy of ±5 ppb ±5% of reading.
Not sure who Hach is marketing theirs to.

I do use the Hanna checker every once in a while and when I detect anything over a couple of ppb I change the carbon filters right away.

Woodyman · May 3, 2022

Muffin87 said:
The HI761 Hanna Chlorine Ultra Low Range Checker is $59 and reads between 0 to 500 ppb with an accuracy of ±5 ppb ±5% of reading.
Not sure who Hach is marketing theirs to.

I do use the Hanna checker every once in a while and when I detect anything over a couple of ppb I change the carbon filters right away.

Not geared to the hobby. Maybe a large importer that is constantly producing RO/DI or am aquarium, this is geared more towards industrial/manufacturing use.

The Hanna meters are sufficient for our general hobbyist use!