TDS out of RO at 20, need DI advice

Rekonn

Rekonn

Premium Member
How many clean gallons can a single DI cartridge put out with 20 TDS input water?

Backround:
I got a TDS meter and tested my water. The tap water starts at 330 TDS and then after passing through my Kenmore Ultrafilter 500 RO system, it is reduced to 20 TDS.

I've been fighting cyano for a long time (increased flow, reduced feeding, etc) but have never been able to fully get rid of it, and believe that my 20 TDS water is the cause. If I'm doing the math right, my current RO provides 94% rejection.

I'm setting up a new 90G tank, let's assume I do 20G of water changes and 30G replace evaporated water for a total of 50G a month. I'm thinking about getting this DI unit. I'm assuming that the color changing cartride that goes with it is this one. At 20 TDS input water, how many gallons of 0 TDS water can I get out of one cartridge? For a reef tank, should I aim for 0 TDS, or would 5 TDS still be low enough to not cause cyano?
 
You might want to replace the membrane with a better one. I'm guessing the one your using is for drinking water.

That's a nice DI cart. I was going to lin you to the same one but I figured I look before I linked:D

FWIW, I use 2 DI carts after my RO.
 
Yes, that RO is for drinking water, it looks exactly like this one . I didn't know that you can mix and match parts, are they all one standard size? Could I just get this membrane and expect it to fit? Should I replace the filters I have in there now too?
 
<a href=showthread.php?s=&postid=6941088#post6941088 target=_blank>Originally posted</a> by Rekonn
Yes, that RO is for drinking water, it looks exactly like this one . I didn't know that you can mix and match parts, are they all one standard size? Could I just get this membrane and expect it to fit? Should I replace the filters I have in there now too?
Click to expand...

I've never seen one of the units but the better membrane should, probably, most likely fit. I'd also replace the sediment and carbon block filters too and then add the DI. If you add the DI without replacing the others you'll use the DI resin up a lot faster.
 
Ok, even though I'm still not sure if the new filters and membrane will fit in my current RO, let's assume for now that they will. I'm at 94% with my current system, and I'd guess I'd be at 98% after the upgrades. So, instead of 20 TDS water coming out of my RO, I'll have 7 TDS. No doubt that is better, and the DI cartridge will last longer, but is it worth it? How much longer will it last? Since 7 is ~1/3rd of 20, does that mean the DI cartridge will last 3 times as long?

And as for my original question, there's gotta be a chart or something showing DI cartridge performance vs input water. Help me attach some numbers to this so I can determine whether it's worth it to spend $80 on a new membrane and filters in addition to getting a DI unit.
 
From AWI FAQ "The capacity of the cartridge is 6,800 ppm. Measure the TDS of the water being produced by the membrane (after the membrane). Divide that result into 6800, the answer is very close to the number of gallons you can expect to get from the DI cartridge."

So 6800/20=340 gallons
6800/7=970 gallons
 
Thanks, that's exactly what I'm looking for. Funny that it's in the faq and not on the product details page. If I buy the refillable kit, that works out to about $15 per cartridge (with shipping). At 50 gallons per month my current setup isn't bad at all, I can get 7 months worth for $15. If I upgrade I'll be up to 19 months for $15. I think I'll just use up current membrane and filters, and then get the good stuff when they're due to be replaced.
 
I tested my faucet water again today, and it was at 600 TDS! The water coming out of my RO was at 45 TDS. At first I wondered if my meter was off, but then I tested some RO water from just a couple days ago, and it was under 20 TDS. Is it possible for my water supply to fluctuate that much? To go from 350 to 600 TDS a couple days later? (btw, I live in AZ)

I tried to do some more research on my RO system, a Kenmore Ultrafilter 500 in an effort to replace the membrane with a better one. I called up 3 different Sears numbers and one Kenmore number. Everybody could sell me the unit and replacement parts, but nobody could tell me a damn thing about it! The most information I got was that the unit as a whole (not just the membrane) was rated for 12 GPD.

I always thought my system was slow, but man, can that be right? Also, the price for the RO membrane was $60 + S&H. The Filmtec 75GPD membrane on the purelyh20 (great site AZDesertRat, thanks!) is only $40. The 1 micron sediment filter and 1 micron carbon block are $11 together wheres the Kenmore pre and postfilter pack is $35. So I'm thinking my RO system is overpriced, wholly inadequate for reefkeeping, and I'm probably better off just getting a new RO/DI system.
 
You will find here in the Valley the norm will be 550 to about 800 most of the time. This is due to the changing water sources and blends between the Salt River, Verde River and CAP or Colorado River water. It can vary day to day as Salt River Project changes the blends it supplies through the canal system.
Its true replacing all the filters and membrane can be as expensive as a complete new unit in some cases.
 
Rekonn,

My RO TDS is 21-24. This is after AWI sent me a replacement as the one before was the same. My tap water is around 250 or so. I just quit fussing with it and change the DI when it gets to 2 or so. I still get lots of water between DI changes and as long as the final product is 0, I have learned to live with it.
 
<a href=showthread.php?s=&postid=6968761#post6968761 target=_blank>Originally posted</a> by old salty
Rekonn,

My RO TDS is 21-24. This is after AWI sent me a replacement as the one before was the same. My tap water is around 250 or so. I just quit fussing with it and change the DI when it gets to 2 or so. I still get lots of water between DI changes and as long as the final product is 0, I have learned to live with it.
Click to expand...

What RO membrane are you using?
 
Dow Filmtec - both were provided to me by AWI. The first came with the Typhoon III and the second was a replacement filter.
 
General Information that might help you chuck and I from air water and ice talked for over an hour a few weeks ago and he suggested you get a pressure gauge and test the pressure if the pressure goes down it is time to change the catridges not the di the di last quite a while it is more in the catridges that you use and watch your pressure gauge if it starts going up then the ro needs to be changed just infor for what it is worth
 
A 94% rejection rate for your membrane is very good. A 100 GPD filtec membrane is supposed to have a 90% rejection rate and a 75 GPD membrane is supposed to have a 98% rejection rate. Besides the places already listed the filter guys
http://www.thefilterguys.biz/index.htm
is also a good place.
 
You must log in or register to reply here.

Similar threads

dogstsx
NEED HELP WITH RO/DI SYSTEM
2
Replies
34
Views
435
griss
griss
Mr31415
RO unit: DI resin depletes quickly
2
Replies
25
Views
1K
Mr31415
Mr31415
H
RODI Questions, comments on some odd things with my system
Replies
5
Views
569
born2lovefish
B
Raptor72
Another RO/DI setup question(s)
Replies
17
Views
150
griss
griss
R
Seattle area water at 28 TDS from tap. Need RO?
Replies
7
Views
436
jason2459
jason2459
Back
Top