RO/DI When to change and which filters need changing.

[Legion Aire]

I live in an area that has the worst water I have ever tested. All of my filters and resin were replaced almost 6 months ago. I figured I was going to change the three stages before the membrane, at the six month stage, but now I am thinking I may be waiting too long and am running the risk of damaging the membrane or the resin.

I have a six stage RO/DI 75gpd system I purchased from BRS.
The first stage is a 1 micron sediment filter.
The second stage is a 5 micron carbon block.
The third stage is a 1 micron carbon block.
The fourth stage is a 75gpd membrane (98% rejection rate)
The fifth and sixth stages are filled with DI resin.

My testing results as of today are:
Water pressure 75psi
At the tap 1250ppm
After the RO membrane 8ppm
After the dual DI 3ppm

I guess my question is I am not too sure about which filters should be replaced, I am hoping that I only have to change the first three filters, since it has only recently begun to even register anything coming out of the DI. The membrane has always had about 3-5 ppm.

 

[Legion Aire]

No one???

 

[caudill187]

My local water comes in at much lower PPM and I have never tested the water coming out of the Membrane. I only have a 4 stage system. I change the DI resin when my output TDS starts rising at all. I use color change resin and this seems to happen a few weeks after the color has changed. I feel like if it stays below 10, I'm OK but certainly time to change. It goes back to 0 after I change the DI resion. I change the particulate filter when it is visibly very dark and change the carbon block about once for ever two particulate filter changes. Of course, I only change the Membrane once a year or so, when I find that my DI resin is lasting a shorter and shorter period of time.

Hope this helps.

 

[AZDesertRat]

Manufacturers recommend changing the sediment and carbon block filters every 6 months regardless of usage. You should also be monitoring your pressure gauge looking for a change in head loss or restriction in pressure available to the membrane reducing its rejection rate or removal efficiency. After a 3-4 or so psi drop in pressure it could be costing you money in DI replacements since the membrane is not working as well as it should be.

Scrap the second unneeded carbon block and turn it into an additional DI filter for best bang for your buck or eliminate it all together, all it does is cause additional pressure loss to the RO membrane which is not productive.
Then replace the sediment with a 0.5 micron absolute rated sediment filter and the carbon with a 0.5 micron, 20,000 gallon carbon block and the first DI with a SilicaBuster reef specific 20 oz DI cartridge.
You can get the full replacement kit here for $52:
Untitled Document

FILTKIT-3PK-CSPDI​

CSPDI Filter Replacement Kit ​

​

$52​

It will do a much better job of protecting your RO membrane so it will last longer and work better which in turn protects your DI resin better, gives you better water quality for much longer and costs you less money in the long run. The RO membrane should last 3-5 years or longer as long as you keep up with the filter replacements and use high quality low micron replacements.

 

[Legion Aire]

Let’s see if I understand this, I should be reading the pressure after the third stage, before the membrane.
The filters should be in this configuration.
1^st stage .5 micron sediment filter
2^nd stage .5 micron carbon block
3^rd stage DI Silicabuster cartridge
4^th stage 75gpd membrane
5^th and 6^th stage DI resin

Does this sound correct? I will not be able to run this configuration because I already have replacements for the current filters, I will be ordering these other filters for the next changing. Do you think I should have to replace the membrane or resin or just the filter and carbon block?

I have never used the color changing resins because I was told they contain certain types of dyes that leach out into saltwater. I thought they would be more user friendly but didn’t want to risk it.

 

[AZDesertRat]

No.
1. 0.5 micron sediment filter
2. 0.5 micron carbon block
3. RO membrane
4. SilicaBuster DI
5. Mixed bed DI or additional SilicaBuster

You will remove or replumb your existing 3rd stage carbon canister. You can leave it attached to the top bracket you need to unscrew the nipple between the 2nd and third canisters and move the line from the third canister up to the RO membrane housing over to the OUT on the second, now 0.5 micron carbon block. You will then rotate the third canister 90 degrees and replumb it so the treated RO water now enters the canister from the back then goes out the front and into your other DI canister(s).

You are correct, color changing DI resins do contain dyes that wash off when the resin is exhausted causing the color change. These dyes are not real accurate and actually show up as TDS in the finished water as they wear off. The changes can be in streaks, layers, too late, too soon, not at all, etc so a good handheld TDS meter is a much better indicator.

 

[VegasRick]

+1 to what AZDesertRat said.
With 2 DI you should be getting 0 TDS and its time to change the resin when you start getting anything above that.

 

[Legion Aire]

Ok I understand a lot better now. I will be changing all the filters, membrane and resin.

Are the filters from the site you sent me to, Spectrapure, compatible with my BRS RO/DI unit?

Where should the pressure gauge be placed?

 

[AZDesertRat]

Yes, they both use standard size 10" replacements.
The inline pressure gauge goes after the carbon block, before the RO membrane so you can monitor pressure loss due to plugged filters.

 

[MBG75]

If you have 1250 at the tap, and 8 after the membrane..the membrane is still good. 98% rejection rate means with a 1250 tap reading, 25 and under is acceptable coming out if the membrane.

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