RO/DI Questions

Dustin1300

Dustin1300

Reefaholic
I just replaced filters in my RO/DI and finally put a TDS meter in place so I can more easily track when to change filters. Right now here is how my filters are in order:

5 Micron Sediment Filter -> Carbon -> Carbon -> Membrane -> DI -> DI

I have the IN/OUT of the TDS meter before and after the DI so I know when to replace the filters or DI. Right now I'm getting about 18-19 before the two DI cartridges and am getting 0 on TDS after the DI. This is after just about 2 gallons of water going through but think this might drop after more water has been processed.

Anyways, my questions:

- Should my TDS be lower before hitting the DI?

If so....
- What should I put before the DI to cut down on the TDS so I don't go through so much DI refills? More carbon or another sediment filter before my first stage?
 
What's the TDS of the tap water, and what kind of membrane does the unit have? Is it a 75 gpd membrane? They should reject about 96-98% of the tap water TDS.

Neither carbon nor sediment filters will reduce the TDS. You might need to add a degassing phase, or the RO membrane might be having some problems.
 
After going and checking after 5 gallons of water it seems that the TDS reading is 10-11 before the DI. I'm unsure of the TDS reading on the tap as I have the two Ts off of the locations I earlier described.

In regards to the membrane, I'm using 125 GPD membrane and it is brand new. My other was nearly 2 years old and was time for a new one:)
 
The 100 gpd membranes tend to be very leaky, if they haven't changed recently, so that level of TDS isn't all that surprising. We'd need a tap TDS reading to be sure, though.
 
Bad to hear....I guess I should have just researched RO/DIs a bit more before I replaced the filters. I just did a bit more research and found what you are stating with the 75 GPD having a 98% rejection rate and 100 GPD having around 96%. I guess I'll just burn through DI for a while until I decide to get ANOTHER membrane.
 
Dustin1300 said:
Bad to hear....I guess I should have just researched RO/DIs a bit more before I replaced the filters. I just did a bit more research and found what you are stating with the 75 GPD having a 98% rejection rate and 100 GPD having around 96%. I guess I'll just burn through DI for a while until I decide to get ANOTHER membrane.
Click to expand...

don't forget to change the flow restrictor too to match the membrane flow.
 
I think 96% is possible only with higher pressure, as well, but I haven't checked all the statistics for a bit. The Dow Filmtec runs more like 90% rejection, from what I can tell from the various web sites, but it'll take some more checking.
 
The Osmonics requires a higher pressure (65 psi) and might not meet 96% rejection with standard house pressure. I'm not quite sure how well it'll work.
 
higher pressure better clean vs.dirty water percentage .and yes make sure when your using a different gpd membrane that you also change the restrictor or you will have problems .
 
its pretty simple to move your in probe from your tds meter to get your source water reading. as long as the line going into your ro/di unit has same size tubing as rest of system. i say that because i started out with a small coralife unit & the input tubing was bigger then ouput tubing. if its all the same just cut a small piece of tubing from output or where ever you can spare , & hook the probe up there.have the small piece running in a bucket or sink for several gallons. check the tds from source & then just move probe back to where you want it. thats how i check my source water. i did it about every other time i made water to begin with. to see if it changed any. now i just do it every other month
 
I dont have much to add, but I have a 5stage plus BRS RO/DI unit.

the TDS reading pre-di canister is usually about 4-7 and after it is 0.
 
From what I can tell the membrane is a TFC from Purewater Club. I was still a college kid when I entered the hobby three years ago but have more money to invest now. Would you recommend replacing the whole RO/DI unit down the road rather than just replacing the membrane and flow restrictor?

Maybe I can just make use of the one I have now and remove the DI stages for my drinking water/fridge.
 
maynardjames said:
its pretty simple to move your in probe from your tds meter to get your source water reading. as long as the line going into your ro/di unit has same size tubing as rest of system. i say that because i started out with a small coralife unit & the input tubing was bigger then ouput tubing. if its all the same just cut a small piece of tubing from output or where ever you can spare , & hook the probe up there.have the small piece running in a bucket or sink for several gallons. check the tds from source & then just move probe back to where you want it. thats how i check my source water. i did it about every other time i made water to begin with. to see if it changed any. now i just do it every other month
Click to expand...

I would have to put a T on the source to put the probe in....I'm going to the basement now and going to test:)
 
Okay....After doing a bit more testing here are the results of probe in different locations after running water about 10 minutes:

- Before Unit - 407 ppm
- After RO/Before DI - 10 ppm
- After DI - 0 ppm
 
That TDS level is fairly high. The membrane is doing well enough. I might measuring the pH of a up of tap water, then aerate it outside for a few hours, and measure again. If the pH changes much, a degassing column might help.
 
bertoni said:
That TDS level is fairly high. The membrane is doing well enough. I might measuring the pH of a up of tap water, then aerate it outside for a few hours, and measure again. If the pH changes much, a degassing column might help.
Click to expand...
jonathan, do you know of any pictures or drawings of anyones degassing columns? i need to set one up bad to save on di
 
Don't mean to hijack the thread but I have a simaler problem with useing up di way to fast. My TDS of source water is 780tds after membrain it's 85tds and I only get about 100g of water out of a DI change. Is my membrain bad? Or is this something I just have to live with because of the insane TDS of the source water?
 
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