RO vs RODI

rw135

New Member
Hi there, new to posting.

Is there any difference between RO water at 0 TDS and RODI water at 0 TDS? I run my water filter system and found that my RO comes out at 0 TDS already. Do I "get" any advantage with the DI if it's already at 0?

Thanks.
 

lmforbis

Well-Known Member
If it is truly 0 TDS there probably isn't a need for DI resin but it may not always be 0 TDS. There could be seasonal differences in dissolved solids in your water.
 

rw135

New Member
Thanks. The line after the RO filter reads 0 on the TDS meter, so I didn't think I needed to go thru the DI.
 

rw135

New Member
If / when the readings start moving above 0, that should mean it's time to change the pre-filters? or start flowing to the DI and check and see if that moves above 0.
My input reads are in the 130's TDS range.
 

bang guy

Moderator
You may as well just send it through the DI. The cartridge will not be used if there's nothing in the water and will last a long long time but if anything ever starts to show up it will remove it.
 

rw135

New Member
Thanks for the advise.
I guess sending it thru the DI wouldn't use up the resin if it was at 0 in the 1st place.
 

2quills

Well-Known Member
Once the filters start getting some use the tds will start to climb. I'd still recommend a DI stage.

You're lucky. Our city water is so nasty I usually have 14-18 tds after the membrane. Even on a fresh one.
 

streamer

Member
I only run a RO unit, my tds are about 10ppm and it feeds 2 tanks, a 125 gal fowlr w/55 gal sump and a 75 gal mixed reef w/55 gal sump and my tanks are AWESOME... no issues.. oh, in the fowlr I run a VERY heavy bio load and I tend to over feed..and to be honest, there is probly a heavy bio load on the 75 as well...
 

snakeblitz33

Well-Known Member
I would personally run one just in case there are any changes. If there is, then you should visibly see it as the DI resin changes color.
 

rw135

New Member
At what point does one start seeing a "rise" in TDS. Does anyone have a rule of thumb for the range a filter will last??? I've only had the filter system for about 9 months now.
 

bang guy

Moderator
Right, the cleaner the source water the longer the filter cartridges will last. I also replace sediment and carbon every 6 months. The DI is replaced once I detect TDS over 1. RO is every few years depending on how it's working.
 

pegasus

Well-Known Member
Fortunately, the RO membrane... which happens to be the most expensive component... should last about 3 years. It depends on your filter change routine, and if you use a flush kit. Dirty or leaking filters and no flush kit will kill the RO in short order.
 

snakeblitz33

Well-Known Member
My tap water TDS when I bought my unit was anywhere from 500 to 999+ and the filters lasted anywhere from two to three months...

Then I moved and my tap water TDS sits at around 250 TDS and the water company does a chlorine burn three times a year, so I still have to replace my filters every three months.
 
My neighborhood has a community well and we have hard water at a 17 grain and my TDS before my softener is about 470 tds and after my DI it is 0. I havent checked what it is after my RO membrane...I need to hook up the meter to it. I know I had to replace my DI resin after the first 50 gallons. I added a 2nd DI chamber now. Thats the beauty of the RO units....you can upgrade them super easy and pretty cheap. My unit cost me $85 on eBay for a 4 stage and I added the 5th stage for $22.
 
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