RODI rant

[jd371]

Why is it that every time I try to change out some of the filters I struggle to get it back to 0 TDS again. I have a 6 stage filter with close to 60 psi coming out of the tap at 32-35 TDS. I was getting 2 TDS after the RO and 0 TDS after the dual DI before I changed the filters. The RO (dow75gpd), sediment, carbon block filters were replaced before the summer along with the DI resin. The carbon block filters probably have another month or two left in them but the sediment filter was dirty and brown so that's why I decided to change all three now. After flushing the carbon blocks and letting the RO flush for over an hour I'm getting 3 TDS out of the RO and 2 TDS after the DI's even though there's hardly any color change in the resin and still good. :mad:
This not the first time this has happened. It seems whenever I just need to change one or more filters I have to go through this every time and wind up changing all of them to get it working right again. The RO's are supposed to last 1-2 years but I'm lucky if I get 6 months out of it, I went ahead and ordered another one.

 

[Ridgeway]

Are you sure you are packing your DI resin canister correctly and that water is channeling through it ?

2 or 3 TDS output from the membranes is absolutely fine and i see no issue there, it's only that you're not getting any benefit from your DI ie 3 down to 2 TDS which to me means the water is actually not being effectively final filtered.

I'd repack the DI canisters.

 

[madweazl]

Additionally, if the tap is 32-35, your post RO should read 0. You sure it is plumbed correctly?

 

[Ridgeway]

Additionally, if the tap is 32-35, your post RO should read 0. You sure it is plumbed correctly?

Not really, any RO membrane will always leave a few TDS in there, they are just not capable of removing everything. The 2-3 he's getting is reasonable enough. The fact that the feed water is very good (32-35 TDS) will actually mean that the membranes could last longer if correctly used.

 

[JoshH]

Not really, any RO membrane will always leave a few TDS in there, they are just not capable of removing everything. The 2-3 he's getting is reasonable enough. The fact that the feed water is very good (32-35 TDS) will actually mean that the membranes could last longer if correctly used.

I don't entirely agree with this statement. My dual RO membranes put out between 0-1 TDS with 240ish incoming. If his incoming TDS is only 32, 3 TDS means a rejection rate of barely over 90%. I don't know of anyone who would say there membrane is fine with that kind of rejection rate. That's a worse rejection rate than even the cheapest membranes on the market and certainly below a standard membranes suggested replacement rate.

However, there are plenty of people who do have to deal with much higher TDS after the membrane because of high incoming TDS. So in that regard, 3 TDS is certainly better still than what some have to deal with, but it still means he will be burning through DI resin at roughly 3 times what he is used to.

I do agree that with a freshly packed DI canister, it should be bringing that 3 to 0 and there is probably some form of channeling going on.

 

[jd371]

Are you sure you are packing your DI resin canister correctly and that water is channeling through it ?

2 or 3 TDS output from the membranes is absolutely fine and i see no issue there, it's only that you're not getting any benefit from your DI ie 3 down to 2 TDS which to me means the water is actually not being effectively final filtered.

I'd repack the DI canisters.

I have a 3 pack of prefilled canisters. The thing is that both DI resins are good with hardly any color change and were working fine before I replaced the three filters. I went ahead and replaced one of them to see and still getting 3 and 2. I don't want to replace the other one because like I said it's still good and was working before I changed the filters so there's no point changing it.

 

[Ridgeway]

Prefilled canisters, how do you know if they were packed correctly ?

So could it be that the one you replaced was actually working correctly and the other not, and now you've replaced it with another poorly packed canister ?

 

[Jeeperz]

I buy from spectrapure. With their upgraded ro membrane. My TDS is 90-100 in, 0-1 out. Not sure what would cause other issues. Is it a manual flush or auto? Maybe check the restrictor tube for plugging.

 

[Ridgeway]

I don't entirely agree with this statement. My dual RO membranes put out between 0-1 TDS with 240ish incoming. If his incoming TDS is only 32, 3 TDS means a rejection rate of barely over 90%. I don't know of anyone who would say there membrane is fine with that kind of rejection rate. That's a worse rejection rate than even the cheapest membranes on the market and certainly below a standard membranes suggested replacement rate.

However, there are plenty of people who do have to deal with much higher TDS after the membrane because of high incoming TDS. So in that regard, 3 TDS is certainly better still than what some have to deal with, but it still means he will be burning through DI resin at roughly 3 times what he is used to.

I do agree that with a freshly packed DI canister, it should be bringing that 3 to 0 and there is probably some form of channeling going on.

It's not a question of rejection rate but a question of what TDS level membranes can get down to, 2-3 is pretty good and i wouldn't expect 0 TDS just because the input was 30ish.

 

[jd371]

I replaced the other DI resin and I'm still getting 3 and 2, I'm beyond frustrated! I didn't need to touch these because they were both working fine before I replaced the filters. I don't see how just replacing the sediment and two carbon blocks would cause this if nothing was touched after those.

 

[alton]

When I could not get 0 out of my DI I realized my water was leaking past the rubber gasket on top. So I now run two rubber gaskets and no water flows past my DI resin. Back to 0.

 

[JoshH]

It's not a question of rejection rate but a question of what TDS level membranes can get down to, 2-3 is pretty good and i wouldn't expect 0 TDS just because the input was 30ish.

Well my membranes can get 240+ TDS down to 0 so your arguement doesn't make much sense. If his rejection rate is 90% to me that's a failed membrane, doesn't matter if the TDS coming out of it is 3. Yes 3 TDS is totally something DI can handle with no issues and some people have it much worse. But If his membranes were new or even a year or two old I would absolutely 110% expect nothing more than 1 TDS coming out of them with 33 TDS going in.

@jd371 are you on a well or city water?

 

[jd371]

When I could not get 0 out of my DI I realized my water was leaking past the rubber gasket on top. So I now run two rubber gaskets and no water flows past my DI resin. Back to 0.

Dude, I want to buy you a beer!!! That did it, I'm getting 3 and 0 now after adding the extra gaskets. I always check them too to make sure they're good and seated properly.

@jd371 are you on a well or city water?

I'm city and from what I've heard we have pretty good water. Even when new the membrane never went below 2. This is what I use.

 

[JoshH]

Dude, I want to buy you a beer!!! That did it, I'm getting 3 and 0 now after adding the extra gaskets. I always check them too to make sure they're good and seated properly.


I'm city and from what I've heard we have pretty good water. Even when new the membrane never went below 2. This is what I use.

Glad you got your issue fixed it sounds like you have pretty good water, do you know if they use chlorine or chloramines? If chloramines, are you using the appropriate carbon blocks ?

 

[jd371]

Glad you got your issue fixed it sounds like you have pretty good water, do you know if they use chlorine or chloramines? If chloramines, are you using the appropriate carbon blocks ?

I believe we're just chlorine, but I will look into it to see if they use chloramines also. I'm using the 5 micron chlorine & VOC and the 1 micron Matrikx CTO Plus from BRS.

 

[JoshH]

I believe we're just chlorine, but I will look into it to see if they use chloramines also. I'm using the 5 micron chlorine & VOC and the 1 micron Matrikx CTO Plus from BRS.

Certainly worth a look, Chloramines will burn through regular carbon blocks MUCH faster than chlorine will and if this isn't caught before they exhaust it can lead to premature membrane failures.

 

[madweazl]

Not really, any RO membrane will always leave a few TDS in there, they are just not capable of removing everything. The 2-3 he's getting is reasonable enough. The fact that the feed water is very good (32-35 TDS) will actually mean that the membranes could last longer if correctly used.

They should be in the 98%+ range so it will come out <1 (roughly .4 but the meter will read 0). If it's anything but 1, there is likely an issue with the RO membrane (or the meter is no good). Our tap water is typically in the 100-102 range and I typically see 0 post membrane (1 occasionally). While the DI is doing its job now, something still seems off with the RO membrane (or the meter).