RODI not reading 000tds

Hi guys,
Been setting up my static RODI system at home. I’m using a 1micron sediment filter, to a 5micron carbon block, to a 100GPD RO membrane, to a 10"x2.5" DI cartridge, been running my mains water through it which is approx. 370ppm TDS (poor i know)

Mains pressure is plenty good, but I’ve been getting around 3L or 0.80GAL an hour from the RO (only 72LPD/19GPD) at a TDS of around 18-19ppm, then the DI takes it down to only 14-15ppm…
Im pretty sure its all set up right, I’ve done heaps of research into it all, and been troubleshooting this problem.

So what am I doing wrong??

Sounds like you need a higher flow RO, I believe mine is 1200 GPD. I also run dual 20" DI cartridges. With a TDS as high as yours, you might want to try running bigger filters. RO filters seem to like higher pressures, around 100psi or so. Hope this helps.

Hi! Thanks for that info, that makes it alot clearer!
Im waiting on a couple of water pressure gauges to come in the mail, and I’ll make sure I check the temp when they come too.
Also Russ, out of curiosity, comes up with no additional shipping costs to AUS, is this correct?
And would it be viable to install a second 100-150gpd membrane parallel to my currant 100gpd one, along with a second cartridge of DI resin? (I have a couple of filter housings spare) would that make any difference?

Sam … the most likely reason is that your DI Resin is shot … dead … maybe dried out …

What resin did you get ? 60/40 MBR ?

The reason that it is delivering a small result is that one side, say (+)ve, is likely exhausted … and the other side, say (-)ve is still partially effective.

If your resin is not dead, then the water is ‘tracking’ … maybe your resin cannister is on its’ side, and the water is running along the bottom of the cannister … and not actually fully exposed to all the resin … this is why the guys using EZY-PURE’s in horizontal can shake their resin and it works again … DI should be vertical for long-life.

What else can you detail ?

Hi Perry, I just got an 8L bag of mixed bed resin (from WWWCS - WWW Cleaning Supplies - Window Cleaning Supplies and Products - Australia - World Wide) thats used in their WFP DI tanks.
The branding on the bag that it came in is Thermax - Tulsion Ion Exchange Resin. The product no is MB-115 (dont know if that makes any difference…)
The DI canister has been kept upright, I learnt about that while researching RO DI etc etc etc.
Might open it up and see whats going on inside and just change it… ive got 7.5L of the stuff left haha

Hi Sam … I am not a fan of Thermax Tulsion … it is made in India and is cheap compared to the USA made Purolite MB400 - we lost a lot of customers when we switched to Tulsion a couple of years ago … It may be a great product now, but I have the bad taste myself. Is the resin dry ? Then it would be most-likely finished. Is there a date on the bag ? Change it out - and if that does not work, you need to buy some new resin … Are you in Melbourne ? If so … you should read the MYTHBUSTER article … you can see it in Notes on our ‘Water Fed Pole Talk’ FB page - or in the latest Window Cleaning Magazine ( Window Cleaning Magazine) - you may find that you do not need DI Resin at all …

Yeah, I just bought the easiest one to get my hands on, and that resin from WWWCS was the easiest, cant seem to find anywhere else that sells it in enough quantity, at a low enough price, and online, in Aus. Theres no date on the bag, but the resin is pretty…well…moist? slippery? haha
Nah, Im about an hour south of Adelaide.

Well today I got a couple of fittings in the mail, (along with my Mk3 Aqua-dapter!) so I fiddled with my set up, I’ve got the RO running to two DI cartridges, which has finally given me a TDS of 000! Hurrah!
The volume is still pretty weak, working out to about 200-250L/24hrs… when it needs to be more like 100gal/370L odd… So I’m in the market for a larger RO membrane, looking for a 40"x4" membrane, that should give me a bit more GPD haha.
Thanks to everyone who commented, your time and help were very much appreciated!

It sounds like you have two issues: DI water isn’t 0 ppm, and RO is producing water too slowly.

If working properly, your RODI system should be delivering 0 ppm TDS water. Your RO membrane is showing a 95% rejection rate, which is better than typical for some brands of 100 gpd membranes. So your membrane is doing it’s job in terms of cleaning the water. Your DI resin may just need to be replaced. With good quality resin, and making some assumptions about your feedwater (no co2 issues, no chloramines, etc), you should be getting about 300 gallons from a single DI refill.

Concerning how slowly the system is producing water, first plug your feedwater temperature and water pressure at the membrane into the calculator at and see what you should be getting out of your 100 gpd membrane. Production speed is very much affected by water pressure and water temperature. If the calculator says you should be getting water much faster than you are, remember that slowed production is one of the two common signs of a membrane that needs to be replaced.
Russ @ Buckeye Field Supply.

I only got a 100gpd one as it should be all I require atm… I found higher gpd membranes similar to yours, but cant find housings for them for the life of me!
Even still, the RO I have now should really be outputting 100gpd, and at 000TDS, especially with the DI?
I’ll try using my 70psi pump through it, see if that makes a difference.
Also, would I be able to run a couple of similar RO filters parallel? Maybe that would help…

With the amount of $$$ I’ve spend already I might as well have bought a setup outright!