When to change RO/DI components?

[pseudorand]

I know this question has been asked many times (links below), but the answers (like most things) aren't straightforward. So I'm hoping to write a sort of summary article and get corrections.

Change components when:

• Sediment filters:
  • Input pressure drops
  • Every 6-12 months, but they're the cheapest part, so just do it often
• Carbon block:
  • Chlorine from waste water measures >0.5ppm
  • At least yearly, possibly more often
• DI Resin:
  • Color changes from dark blue to brown in 75%
  • Color is king, ignore time
• R/O membrane:
  • TDS out > 0
  • Every 1-2 years

And some assumptions:

• Pressure gauge should be installed after sediment and carbon, before R/O membrane
• TDS meter should be installed after R/O membrane and before D/I resin, though many will take readings both before and after DI

Questions:

• How does water flow through the DI resin?
  • The bottom 1/2" of mine is brown with ~11" above still blue/black. How do I know there's not a bunch of brown near the center that I can't see?
• Per the BRS article (below), you have to run the system for 1/2 hour before taking the Cl reading.
  • Does anyone actually do this?
  • If you don't, will Cl be higher or lower?
  • The BRS article says to leave the strip in for 2 minutes and wait 10 minutes for color to develop. My Cl test says to leave the strip in for 2 seconds and wait 10 seconds for color. Is that just a mistake in the article or on my test kit? Do they have a different test kit?
• Does anyone do regular water test of any sort in their R/O water before adding salt?
  • What do you test for and why?
  • How often?
  • Have you ever identified a problem? What was it and where do you live (i.e. what's your water supply)?
• Does anyone change individual components, or just change the whole thing?
  • The components are cheap relative to everything else we buy, and more so if you buy the BRS replacement kits. Does everyone just buy the kit and replace everything (or at least everything other than the RO membrane) at once?

Resources:

• https://www.bulkreefsupply.com/content/post/howto-know-when-to-change-your-rodi-filters
• https://www.reef2reef.com/threads/new-filters-ro-di.842074/
• https://www.reef2reef.com/threads/is-it-time-to-change-my-di-filter-photo.844790/
• https://www.reef2reef.com/threads/di-resin-changing.851778/

 

[shwareefer]

DI Resin:

• Color changes from dark blue to brown in 75%
• Color is king, ignore time

Forget this entire idea and get a dual inline TDS meter. one sensor after RO, one sensor after DI. Preferable follow the second sensor with another DI and move it forward when the first one starts showing .001. Don't buy expensive colour changing resin anymore.

 

[pseudorand]

I have the dual inline, and I get 3 TDS in and 0 out, so I suspect my DI resin is still ok but I need to replace something else, possibly my RO membrane (though it's only just over a year old).

As for the cost:

• Color changing: $14.99
• non-color changing: $11.99

And it last me at least 6 months. I suspect the additional cost of color changing resin isn't what will make me take down my tank.

What do you have against the color-changing resin?

 

[KStatefan]

What is the tds of the water prior to the membrane? You need to monitor the rejection rate of your membrane to determine when to replace

 

[pseudorand]

What is the tds of the water prior to the membrane?

No idea. BRS recommends installing the TDS meter before and after the membrane. However , carbon and sediment filters are cheap, so I'm just replacing them.

 

[Uncle99]

I measure the TDS of source.
Membrane should remove 90-95% of the source number.
When you go below 90%, you’ll continuously eat up the resin faster, to achieve that 0ppm number, so change the membrane at 90%.
When DI goes to 2ppm, I change it.
Colour doesn’t matter if you have a TDS meter.
Mine was $20 bucks. I only test out of membrane every 3 months. I test after DI every batch.
The carbon and sediment are cheap, so every 6 months or so.

 

[KStatefan]

No idea. BRS recommends installing the TDS meter before and after the membrane. However , carbon and sediment filters are cheap, so I'm just replacing them.

Where do you have the TDS meter now?

 

[pseudorand]

Where do you have the TDS meter now?

I mis-spoke before. BRS recommends it before and after the DI resin, which is where I have it. I get 3 TDS out of the RO membrane and in to the DI resin and 0 out of the DI resin.

However, I just changed my carbon and sediment filters and now I'm flushing the membrane. If I leave the TDS meter on during flush, I started at 80 TDS "in" and 0 out (though there's no water flowing out of the DI during flush, of course). After a few minutes, it's down to 13 TDS "in".

Does anyone know if that's a good way to know if you've done an adequate flush? Should water coming out of the RO membrane be just a few TDS 0 after 10 minutes or so when the flush is complete?

 

[LBReefer]

This was very helpful. Thank you!

 

[KStatefan]

I normally run about 5 gallons down the drain after changing a carbon filter

 

[pseudorand]

I normally run about 5 gallons down the drain after changing a carbon filter

Good point.

After 15 min flush, TDS in was 3. I turned flush mode off and TDS went up to 4, possibly still carbon. I'll dump 5 gal I'm normal mode and hopefully get it to 0. It was at 0 both in and out at one point after the last time I changed filters, but new carbon needs breaking in of course.

 

[Rmckoy]

I’ve always changed sediment and carbon block every month or 2 depending on how often I use it , and the pressure gauge .
lower flow on the gauge indicates restricted flow .

di resin I change when it’s all yellowish/brown colour . And tds measures above 0.00
I don’t have a Inline tds meter so have to manually measure mine with a hand held device .

membrane I change once a year typically in the late summer , early fall .

no reason why just a time of year I chose as a reminder

as everything in my tank has stabilized again I haven’t been doing water changes as often , only top off water

 

[KStatefan]

On my system I monitor pressure before the pre filters and and the membrane to determine if my sediment filter has plugged I have fairly clean (no sediment) water and it has never needed to be replaced based on pressure drop so I just change in annually.

I run two carbon filters and the first is replaced when I consume 2000 gallons and the second at 4000 gallons. I have a 3-way valve installed so when replacing the carbon filters I can flush them so none of the carbon fines make it to the membrane.

I monitor rejection percentage of the membrane and replace it when it is less then 97%. The first one I installed lasted 5 years. The second one three months. I switched to the newer Filmtec TW30-1812-50HR membrane. It has a higher tested rejection rate then the others I looked at. I have my waste:good ratio at about 3:1in the summer when the incoming water is 73° F. That ratio will go up when winter gets here and the water temperature drops 30° F.

I use a Spectrapure MegaMax Di system so i look at tds three places to monitor when to replace resin. When the out of the first resin is 50% of the incoming I replace the resin. When the out of the second resin is not zero it is replaced. I have high CO2 in my water so I am going to add a cation and a anion resins in front of my spectrapure to remove any CO2 left in my water after my degassing chamber.

I have a di bypass installed so no tds creep can reach my di resin.

 

[shwareefer]

I have the dual inline, and I get 3 TDS in and 0 out, so I suspect my DI resin is still ok but I need to replace something else, possibly my RO membrane (though it's only just over a year old).

As for the cost:

• Color changing: $14.99
• non-color changing: $11.99

And it last me at least 6 months. I suspect the additional cost of color changing resin isn't what will make me take down my tank.

What do you have against the color-changing resin?

I have nothing against it if that's all you have. I was under the impression this was a "best practices" list which I think colour changing resin is not. As you can see without your meter you would be throwing away resin that is still fine.

 

[dkfrosty1]

I’ll change it when the little light on the filter sensor turns red

 

[pseudorand]

I monitor rejection percentage of the membrane and replace it when it is less then 97%.

How do you measure rejection rate? I didn't know that was possible with home equipment.

The first one I installed lasted 5 years. The second one three months.

That's a huge difference. Any idea what accounts for it?

I have my waste:good ratio at about 3:1in the summer when the incoming water is 73° F.

How do you measure that? Just collect the waste and measure volume? (Seems like a lot of work, but I have a drain by my tank. If you have to put it in buckets anyway...)

I have high CO2 in my water so I am going to add a cation and a anion resins in front of my spectrapure to remove any CO2 left in my water after my degassing chamber.

How do you measure CO2?

Thanks for the detailed reply.

Every time I think I'm getting close to all the "science" I need for this hobby, someone on R2R corrects me, and me inner nerd pulls out the credit card!

 

[KStatefan]

How do you measure rejection rate? I didn't know that was possible with home equipment.

(Membrane Input TDS - Membrane Output TDS) / Membrane Input TDS * 100%

That's a huge difference. Any idea what accounts for it?

I do not know. I switched to a different membrane and am going to test it monthly and track.

How do you measure that? Just collect the waste and measure volume? (Seems like a lot of work, but I have a drain by my tank. If you have to put it in buckets anyway...)

I just used a gradated cylinder and ran 30 second of waste and good water.

How do you measure CO2?

I used a test kit.

Thanks for the detailed reply.

Every time I think I'm getting close to all the "science" I need for this hobby, someone on R2R corrects me, and me inner nerd pulls out the credit card!