RODI filter change sequence

[chaudhry]

I have a spectrapure 90 GPD unit. Working great! My tds out is less than 5 at this time.
I bought it used from a fellow reefer and has never changed the cartridge.
My question: once my tds starts creeping up and its time for change, which cartridge is the most common suspect. Do I follow a sequence to see which one out of the 3 filters is gone bad. Or I just change all of them at the same time and reset the whole thing.
My limited understanding of the filters, tells me that carbon may be the first one to go. Can i just change that and let the RO membrane and DI cartridge in and if TDS not improving the go for the next cartridge.
How much is color change helpful.
Some guidance appreciated!


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[jason2459]

Good recommendations here and what should be done when changing filters
http://www.buckeyehydro.com/faq/#Q1


I personally am very lazy and don't test for total chlorine which would tell you when the carbon blocks need replaced. Membranes are damaged by chlorine and to a degree by chloramines but the DI stage would exhaust very quickly as well for both.

For a standard 10"x2.5" housing which I'm sure yours is I changed my carbon and sediment prefilters out preventatively every 6 months even if not necessary. Cheap insurance overall.

Membranes I change out every year that is divisible by 3 which is easy for me to remember when to change the membranes out at every 3 years. Again, may be a bit early but keeps it going strong.

DI I used at least 2 stages of color changing mixed bed resins. First stage I would let exhaust and when the second stage got about 80-90% changed I would move it to the first stage. Then put fresh DI into the last stage. Then keep that rotation up. It would insure 0 TDS at all times and not waste the older resin as even though eventually 1-2 TDS will start comming out of it thats still reducing what's comming out of the RO and the second stage reduces to 0.


I just upgraded my system to a larger housing and setup and will keep the same basic concepts but extend the 6 month prefilter change to 1 year. The rest will remain the same.
The Gapper
http://www.reefcentral.com/forums/showthread.php?p=24964950

I would set something up so you can run the new prefilters one at a time for like 5 to 10 minutes each with out it hitting the ro membrane. There will be small fines and other stuff that needs rinsed off with out fouling the membrane for no reason. It explains that in that buckeye hydro FAQ as well.

[BrettDS]

You should be getting 0 TDS out of an RODI filter. If you're getting 5 then that indicates that your DI resin is exhausted. You can also test the TDS out of the RO membrane before the DI cartridge to get an idea of how the RO membrane is doing. That should be a reasonably low number (under 20 would be good)

[chaudhry]

Thanks for the suggestions!
All very helpful. I will work on those lines.


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