RODI - TDS up to 5 after membrane

[Dweezilz]

I've been using my Spectrapure MaxCap 90 since July 2022. My input water TDS is usually 115-130, output after membrane is always 2 after flushing and letting it run for a few minutes (often starts around 17 and goes down), and after DI1 is 0, then 0 after DI2. I have not changed the prefilters or Di's since July. All items are Spectrapure and not knockoffs. I use a Smart Buddie RODI booster so pressure is always at 90psi. So last week I moved my RODI system from upstairs to the basement. Everything seemed fine. I made some more topoff water following the same process as always and the results were the same as always. I have the Smart Buddie flush the membrane 2 or 3 times and then run with a valve shut out of the membrane to divert water until it's at 2 TDS from the membrane. I also have a flow valve after the 1st DI as it will spit out higher (20-30 TDS) for 20-30 seconds. Once that's back to 0, I send the water to the last DI and it's still 0 as always.

Today, my membrane TDS would not go to 2 and it has stayed hovering between 3 and 6 TDS and mostly 5 or 6. It's always gone down to 2 within 5 minutes. I've tested with my hand TDS meter without the Buddie running to confirm that out of the membrane is indeed fluctuating between 3 and 6 TDS. I know for some 6 TDS out of the membrane might not be bad ,but for my setup it's out of the ordinary to have 95% rejection rate. I would figure even if the water in the basement has something in it that upstairs didn't, the 115-130 TDS going into the membrane is the same as always. Can any of you think of a reason for this sudden change after only 7 months? It's not like the basement water is any different than what's upstairs as it's all coming into the house from the same single pipe and total TDS has remained the same of source water. I'm going to buy new pre-filters but could the membrane be going bad already? I don't do that many water changes at all and have only a 65 gallon aquarium. Thanks for any help! I HATE buying random things trying to fix the unknown, but here I go again! ha.

 

[Dweezilz]

Something just hit me that might answer my own question. Since I moved the unit to the basement last week, I'm guessing that the water temperature could be significantly lower than upstairs since it's below ground level. I see that the membranes say 98% and tested at 77 degrees. Is it likely that last week when it was warmer outside, the water temp in the basement was higher thus I was getting 98% rejection and the last few days it's been much colder. Could that colder basement water be what lowered the rejection rate to 95%? That would answer the question I guess if so.

 

[KStatefan]

Cold water will increase rejection rate

Chlorine getting thru your carbon filters can damage the membrane
The membrane drying out can also damage it.

 

[Dweezilz]

Cold water will increase rejection rate

Chlorine getting thru your carbon filters can damage the membrane
The membrane drying out can also damage

I know about not letting it dry out...that didn't happen as over the last 6 months I've often gone a few weeks without making water. The chlorine part is interesting. Would 6 month old sediment and carbon filters all of a sudden become so dirty that they would let chlorine through? Seems odd. We have very clean water and TDS of 130 on average going in. I didn't think I needed to replace them before 6 months and the prefilter barely looks dirty.

 

[YOYOYOReefer]

I fail to see the problem with 6 ? its within the tolerance of the membrane if your source water is 115 to 130
thats right on par for a 95% rejection rate.

any chlorine going thru an ro filter will drastically shorten its life..

How is your source water filtered before it gets to the house? Chlorine? Bromine? Chloramines? makes a difference how you pre filter before your ro membrane. Carbon is great for chlorine, not so great for chloramines.

 

[KStatefan]

You would have to test after the carbon block the verify if you are getting chlorine past the filter.

 

[EricR]

You would have to test after the carbon block the verify if you are getting chlorine past the filter.

Is just testing the waste line acceptable (for chlorine) or is it necessary to pull the line after the carbon (before RO membrane) and test that directly?
*sorry to hijack but seems relevant enough here

 

[YOYOYOReefer]

if you want to test for it a Hatch CN70 test kit would tell you for sure.
but if you dont have access to good test kits, then i would find out how your source water is treated and make sure you have the right prefilters before your RO filter.

 

[KStatefan]

Is just testing the waste line acceptable (for chlorine) or is it necessary to pull the line after the carbon (before RO membrane) and test that directly?
*sorry to hijack but seems relevant enough here

That is where i would test it easy to get a sample

 

[Dweezilz]

I fail to see the problem with 6 ? its within the tolerance of the membrane if your source water is 115 to 130
thats right on par for a 95% rejection rate.

any chlorine going thru an ro filter will drastically shorten its life..

How is your source water filtered before it gets to the house? Chlorine? Bromine? Chloramines? makes a difference how you pre filter before your ro membrane. Carbon is great for chlorine, not so great for chloramines.

I knew someone would question why 6 is bad thus I mention that in my original post. So the question isn't if 6 is acceptable as I'm sure for many it is and maybe even for me is is. I already calculated the 95% which I stated in the original post. The real question is if I have a membrane from Spectrapure directly, that is supposed to be 98% rejection and for 6 months I got 98% rejection and know for fact that TDS was always 2 after the membrane and suddenly for unknown reasons it goes directly to 6 after being 2 TDS just a week or so earlier, what caused that. No gradual loss, just 2 to 6 in a matter of days. I honestly want to avoid just buying expensive things hoping that's the fix. I just want to know what the possible cause is before buying a new $65 membrane and $40 worth of filters . That is the reason for my post. No Chloramines in Cleveland Ohio. Their website specifically says they do not use Chloramines and I called them to confirm last summer. They do use chlorine & floride. No clue about Bromine but it's not listed as one of the things they use. Here is their list of chems used:

 

[Dweezilz]

You would have to test after the carbon block the verify if you are getting chlorine past the filter.

Is there a specific Chlorine test to get or just any of the test strips on Amazon? Also, if there is chlorine getting through, I'd guess previously it wasn't going through since I had 6 months+ of 2 TDS after the membrane. Is there a specific carbon filter for Chlorine or do I just need to replace the carbon filter maybe every 4-5 months?

 

[Calmshadow18]

you could always do an ICP just to back up whatever your seeing, they also make 3 sensor TDS meters which allow you to check each portion of your RODI maker which has been very valuable for isolating which items maybe being exhausted faster. I have mine post carbon, post membrane, and post DI

 

[YOYOYOReefer]

yep change carbon 2 or 3 times a year at least .. its the cheapest safest way to go for your source water for sure.
as long as no chlorine gets to your ro membrane it can last a 12-18 months.

I use the Hatch CN70 test but i have access to chemicals at work.. . if you have a good lfs they probably know about your local water and hopefully could test your water for you.. take them a sample from the tap, after sediment, after carbon, after ro, after di 1 after di2. but really it wasnt broken so just change your carbons more often and change out that ro when it creeps

 

[dwest]

I have the same unit. I replace both the sediment and carbon pre filters every 6 months. I replace the carbon filter to protect the membrane from chlorine and go ahead and do the sediment at that time because it’s easier for me. My membranes will last years (at least 3 or 4) before needing replacing with a similar incoming TDS as yours. My water pressure is about 90 psig and I manually flush the membrane every time I make water. I make about 50 gallons of RODI a month.

This is what works for me.

Edit: I make about 100 gallons per month.

 

[Dweezilz]

I have the same unit. I replace both the sediment and carbon pre filters every 6 months. I replace the carbon filter to protect the membrane from chlorine and go ahead and do the sediment at that time because it’s easier for me. My membranes will last years (at least 3 or 4) before needing replacing with a similar incoming TDS as yours. My water pressure is about 90 psig and I manually flush the membrane every time I make water. I make about 50 gallons of RODI a month.

This is what works for me.

Thanks for the info. I knew people said 6 months 'or so' but figures my luck it lasted 7 months then fouled the membrane to some degree. I wonder if moving the unit somehow dislodged things in the filter? I guess I'll have to replace every 5 months to be safe... 6 TDS out of the membrane is ok but I like 2 better if it saves the DI. Everything in this hobby is an expensive learning experience that's for sure!!!

 

[Dweezilz]

yep change carbon 2 or 3 times a year at least .. its the cheapest safest way to go for your source water for sure.
as long as no chlorine gets to your ro membrane it can last a 12-18 months.

I use the Hatch CN70 test but i have access to chemicals at work.. . if you have a good lfs they probably know about your local water and hopefully could test your water for you.. take them a sample from the tap, after sediment, after carbon, after ro, after di 1 after di2. but really it wasnt broken so just change your carbons more often and change out that ro when it creeps

Thanks! Yeah I'll probably replace the carbon filter every 4-5 months since 7 seemed to be a month too many!
Does the same go for the sediment filter too?

 

[YOYOYOReefer]

Thanks! Yeah I'll probably replace the carbon filter every 4-5 months since 7 seemed to be a month too many!
Does the same go for the sediment filter too?

yes change it it wont hurt

 

[dwest]

Thanks for the info. I knew people said 6 months 'or so' but figures my luck it lasted 7 months then fouled the membrane to some degree. I wonder if moving the unit somehow dislodged things in the filter? I guess I'll have to replace every 5 months to be safe... 6 TDS out of the membrane is ok but I like 2 better if it saves the DI. Everything in this hobby is an expensive learning experience that's for sure!!!

You also might want to get a handheld TDS unit to make your inline monitors are working OK. They do “fail”. I’m not convinced your membrane is the problem, but it is certainly a possibility. I had problems in the past with bypass lines also. I used to have an auto flush valve that failed. So I like to manually bypass and flush now.

Good luck. I’ve always been happy with Spectrapure stuff.

 

[Dweezilz]

You also might want to get a handheld TDS unit to make your inline monitors are working OK. They do “fail”. I’m not convinced your membrane is the problem, but it is certainly a possibility. I had problems in the past with bypass lines also. I used to have an auto flush valve that failed. So I like to manually bypass and flush now.

Good luck. I’ve always been happy with Spectrapure stuff.

I have a handheld and even disconnected my Smart Buddie booster to test water without it in case it was doing something and got all the same readings as the inline. My cheapie Amazon handheld is actually quite good and always matches the inlines at all the points. My Smart Buddie does the auto flush of the membrane itself, but I manually flush after the membrane since it takes more than the 20 seconds of flush to get it down to 2 and then manually after the 1st DI too.

When I got the unit used (lesson learned a while ago, never buy one used) I ended up having to replace the membrane housing because I was getting 14 after the membrane (I think a few of you responded to that post back last summer) and it turned out that the housing was internally not working and leaking waste into good water. That fixed the issue but not before I replaced the membrane twice thinking my process fouled it! That was an expensive lesson on not randomly replacing stuff until you have a very good idea about what the problem is. Trying to avoid that again!! I've learned a ton since then that's for sure.

 

[Dweezilz]

I found this quote from Bruce at Spectrapure. I guess 95% vs 98% is a big difference in DI life. That alone makes me want to fix this issue.

"Also, even more astounding, is that with the membranes that we hand-select and test to insure rejection greater than 98%, we typically see production rates exceeding 100 GPD at 60 psi (and 77 F) !! Why is 1 or 2% so important?? A 2 % increase in rejection from 96% to 98% can double your DI cartridge(s) life. Over the life of the membrane that can save you big $$$ in DI cartridges! That is why our hand selection and proprietary testing (we sometimes reject more than half that do not meet our SPEC of >98.0% rejection) is worth the extra cost. Who else labels their membranes with actual rejection rate on the so called "the same" membrane?"