RO/DI Question

5

58merc

New member
Sorry if this is a commonly asked question, but I’m still a little green when it comes to RO filters.

Right now I have a 100 GPD RO/DI unit. My TDS’s are 198 before and 31 after. Needless to say I’m not happy with the after number. I’d really like to see 0-5ppm.

I know the 100GPD membrane has only a 90% rejection rate. I am looking at getting a 75GPD membrane with a 94-98% rejection rate. My question is what type of numbers should I expect from the 75 GPD membrane? Would a 50GPD be better?

Thanks.
 
with the 75 GPD you should read 0 ppm easily if you get a 98% rejection rate. Assuming you have the common set up with a membrane, 1micron block, carbon block, and vertical DI canister. If you have horizontal DI canister(s) I'd swap them out because they really don't work well. I have the 100 GPD like you with horizontal DI and I'm putting out a TDS of 45 ppm lol. Horrible...I'm ordering the 75 GPD and vertical DI as we speak actually =D
 
My DI a horizontal unit. I know they are not the best. I'll get a vertical one someday. I think I'm going to try the 75GPD membrane first and see how much that helps.

Filter guys have good prices on both membranes and DI canasters. Wish I new about them before, I would have bought my whole system from them.
 
Is that number before the DI or after the DI. Your setup should go like this

1 Micron Sediment

to

1 Micron Carbon

to

RO Membrane

to

DI Canister

to

Tank make up water

If you are showing 31 after the DI then I would definitely replace the membrane and/or get a refill for your DI depending on how many gallons you have run through it. Also if it is new, you need to run 15-20 gallons through the DI and dump it before taking any readings, Fresh DI will always throw out some TDS errors until you run that first water through it. I have a 75gpd Kent Maxima Hi-S Deluxe and I have anywhere between 180 (winter) to 320 (summer) and read Zero on the output from the DI.

Also what pressure are you running at? You should be between 65 and 80psi if you are much lower than 65, you may need a booster pump, and lastly make sure you have a correct sized flow restrictor for that membrane, they are different for each gpd rating on RO Membranes.
 
The filter is somewhat new. I'd guess I've made 75+ gallons with it.

Here's the stages.

5 micron sediment filter

Carbon

5 micron coconut carbon filter? (not sure why that ones there)

RO membrane

DI

Not sure what the line pressure is. It city water and seems plenty strong, but that could be missleading.

Flow restrictor should be right for the membrane, I ordered it as a kit. (I did get one for the 75GPD I just ordered).

The guy I bought it from said it was a set-up for reef tanks. not that it means anything.

Sounds like I'm on the right track. If the new membrane dosen't do it I'll up-grade the DI canaster.

Thanks for all the help!!
Any other advice is welcome.
 
i have a melevs rodi
tds out of sink is 615
tds out of evrything but the di is 44
after di it is 0
615 all the way to 0
cant beat a melevs rodi
 
So I wanted to see, just for fun, what my TDS's were before the DI unit. It turned out to be 62 PPM. Re-hooked the DI and it came out at 26 PPM. Just for fun I turned my horizontal DI unit to a vertical position. Let it run for a few miniutes and re-checked the TDS's. They were 2 PPM!

That's a number I can live with!!

Funny how just turning the DI unit upright had that much effect.
 
<a href=showthread.php?s=&postid=14027188#post14027188 target=_blank>Originally posted</a> by 58merc
The filter is somewhat new. I'd guess I've made 75+ gallons with it.

Here's the stages.

5 micron sediment filter

Carbon

5 micron coconut carbon filter? (not sure why that ones there)

RO membrane

DI

Click to expand...

My guess is the Coconut filter did not protect the membrane well enough from chlorine or chloramines. If you get a new membrane then definitely get some better performing prefilters. A popular membrane is the DowFilmtec 75 GPD.

For prefilters I would recommend a 1 micron Sediment (gradient depth is better than obsolute) and a Matrikx +1 carbon block (1 micron) or if you have lead pipes then get the Matrikx PB+1.

You'll probably want new DI resin too, I've had good luck with keeping the cost down using the refillable cartridges. The online vendors will have a 1 cartridge add-on w/ cannister, refillable cartridge and resin for around $30. You could keep the horizontal as a pre-DI filter if you wanted too.

All of this is available from bulkreefsupply.com, thefilterguys.biz and others.
 
I got a new Film-tech 75 GPD membrane today.
I'll see about ordering some better prefilters. Filter guy's seem to have a good pakage.

My TDS meter I think is a HD brand. It's a pocket tester. I picked it up at a local plumbing supply store. I'm sure it's not the best, cost around $20. In the future I'll up-grade to a before and after inline meter like the one The Filter guys have.

Still reading 2-6 PPM after putting the DI unit upright. I think I'll live with that for now.
Thanks for all the help guys!!
 
Just my 02. I wouldn't use it or wait too long before replacing the prefilters. Chlorine and chloramines can kill a costly membrane fairly quickly.
 
Is your local water treated with chloramine? It's been pointed out to me recently that chloramine isn't as common as I had thought. I think that package looks fine, though. I'd definitely replaced the prefilters and membrane together.
 
If you have Chloramines then the $34 package would be good.

If you just have Chlorine then I would suggest 1 x 1 micron Sediment, 1 x Matrikx CTO/2 followed by 1 x Matrikx +1 (or 2 x Matrikx +1 instead of the CTO/2). The order for installation is important to protect the membrane.

I wouldn't bother with coconut blocks or GAC cannisters. Good carbon blocks are usually superior.

BTW... since your going for 100 GPD to 75 GPD, did you get a 75 GPD flow restrictor with your membrane?
 
With "normal" tap water (i.e., no chloramine) there is really no need for two carbon prefilter stages. One good quality block is enough.

58merc - if you are not sure if your tap water contains chloramines, if you'll tell me the name of your town and state, and the name of your water utility, I'll try to look it up for you.

Russ
 
<a href=showthread.php?s=&postid=14042461#post14042461 target=_blank>Originally posted</a> by BuckeyeFS
With "normal" tap water (i.e., no chloramine) there is really no need for two carbon prefilter stages. One good quality block is enough.

58merc - if you are not sure if your tap water contains chloramines, if you'll tell me the name of your town and state, and the name of your water utility, I'll try to look it up for you.

Russ
Click to expand...

The reason I suggested the two carbon blocks is that the poster has a 5 stage unit. The best obviously would be to convert 1 of the stages to a 2nd DI but didn't want to get there with this one.
 
Understood. In some cases we just recommend leaving that second "carbon" housing empty...

In other cases we can walk folks through turning it into a DI stage as you suggest.
 
Last edited:
Checked with my water dept. today and they DO NOT treat with chloramines. So I got the standard filter package with 1 micron filters. I relise I don't really need all 5 stages, but it can't hurt to throw another carbon block in. I also got an up right DI unit to put in.

Next question, after installing the new membrane (then removing it after your recomendation not to use it untill I get the new prefilters) and reinstaling the old membrane and flow restrictor my automatic shut off dosen't seem to be working. Found this out after the waste water ran all night and all day...Can't wait for that water bill. Anyway, the only thing I did was change the membrane and flow restrictor, then changed it back, went to bed to let my holding tank fill-up. Any thoughts?
 
You may have some air trapped in the ASOV.

With the system running, tilt the entire system so the the ports on the ASOV are vertical, and rap on the ASOV to dislodge any trapped air.
 
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