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RO/DI replacement filters

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    Posted: April 13 2015 at 10:49am
It is time to replace the filters in my SpectraPure® CSPDI RO/DI System. However, I am not sure if I need to replace the membrane as well. How can I find out? I only have an inline TDS meter that came with the unit. Just wondering which filters I need to order.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ReefdUp Quote  Post ReplyReply Direct Link To This Post Posted: April 13 2015 at 10:55am
Usually membranes last 3-5 years depending on pressure and use. You can troubleshoot each filter if you take a TDS measurement before and after each filter. So, take the TDS before the membrane and after. You should get the percentage drop that your filter is rated. If you have a 100 TDS reading before a 98% rejection membrane, then you should have a TDS of 2 after if it is stil good.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Indu Quote  Post ReplyReply Direct Link To This Post Posted: April 13 2015 at 11:31am
Thanks. I located the instruction manual that came with the unit and it explains how I can take the measurements before and after membrane. So far so good. It also talks about 'membrane output calculation' to calculate the expected GPD. I am assuming it doesn't have anything to do with calculation of rejection rate of the membrane. Is that correct?

Thanks again.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: April 13 2015 at 9:50pm
That's correct. It's usually about 4 or 5:1 waste water to purified water, something that can be verified by placing a cup under each line and comparing the amount in the pure water cup at the point when the waste water cup tops up.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Indu Quote  Post ReplyReply Direct Link To This Post Posted: April 14 2015 at 8:39am
Thank you for the reply.

I haven't taken the before and after membrane measurements yet. 

This is a less than 8months old 3-stage unit that I bought new. Haven't replaced any filters/resin yet. I don't see any reduction in water output, which makes me think the sediment and carbon filters are probably okay. However, the inline TDS meter reads 005 on in and 004 on out. TDS is placed after the sediment and carbon filters. So, what needs replacement here? Is my TDS meter reading it correctly? Sorry I am asking too many questions, I haven't dealt with such units before.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bryce Quote  Post ReplyReply Direct Link To This Post Posted: April 14 2015 at 2:39pm
Are you not running DI resin? That is what typically needs to be changed most frequently and is what would most likely get your TDS down to 0. All replacement times on a water filter are going to depend on water quality going in, I have not changed my sediment filter or carbon blocks in 2.5 years, but my DI resin gets changed about every 6 months and I have ) TDS output. If you do not have DI resin, then I would check your TDS before the membrane and after your last stage then you will have a baseline for what your filter is doing, if and when your TDS starts to creep above what your current post last stage TDS is then I would think about changing sediment or carbon, your membrane as Nikki mentioned should last 3 years minimum. Usually a sediment filter can be visually inspected, if it isn't all brown then I wouldn't worry about it. Also if you have not noticed a significant reduction in water filtering time/output those filters are probably fine.

Edited by Bryce - April 14 2015 at 3:38pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Indu Quote  Post ReplyReply Direct Link To This Post Posted: April 14 2015 at 3:16pm
Bryce, 

Sediment filter color is a light yellow. The third stage is DI resin and like you said, I am suspecting that is what I need to replace, not the sediment or carbon filters. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bryce Quote  Post ReplyReply Direct Link To This Post Posted: April 14 2015 at 3:40pm
Yea, I like using BRS (Bulk Reef Supply) color changing resin as its easy to see when the resin is exhausted and needs to be replaced without constantly checking TDS or regenerated (although I just buy new stuff, I don't have the skills Nikki has to regenerate it).
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: April 14 2015 at 4:34pm
AC really ought to be changed every 6 months or so. My understanding is that AC extends the life of the RO Membrane by removing Chlorine, which would otherwise slowly damage the polymer membrane. It also removes molecules that cause bad taste and smell.

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Mark  Hug

BTW, water flow from a membrane that is going bad is typically unchanged from when it was working properly. The only way to tell when an RO Membrane is going bad is when the TDS out of the membrane starts creeping up and passes 20 ppm. If DI resin is used, the final water can still come out close to zero TDS but with all the impurities passing through the enlarged holes in the bad membrane, the DI resin saturates much quicker, decreasing it's usefulness.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bryce Quote  Post ReplyReply Direct Link To This Post Posted: April 14 2015 at 5:42pm
Here is a great video on it changing everything. Looks like I should probably change my carbon filters, they say 6-12 months, but my sediment filter is super clean and my TDS is going in before any filtering is super low.
http://www.bulkreefsupply.com/video/view/howto-know-when-to-change-your-rodi-filters/

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Indu Quote  Post ReplyReply Direct Link To This Post Posted: April 14 2015 at 6:05pm
Just watched the video and realized I could replace the resin myself instead of replacing the whole cartridge. Is that how you people do? Too late, ordered a new cartridge already. :(
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bryce Quote  Post ReplyReply Direct Link To This Post Posted: April 14 2015 at 6:25pm
Yes I change my own di resin. It would depend on if your canister/cartridge is designed to have the DI changed by yourself.
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