Changed ALL RO/DI filters, TDS reading is higher! WTH?

D

dangle

New member
So I'm fighting some algae in my tank and decided to replace all my filters. Before replacing, my TDS reading was 002. Now after replacing the filters it's 011. I've already filtered about 20 gallons of water and it's holding steady at 011. The RO/DI unit is a Water General RD-100 6 stage unit.

I know you're supposed to run it awhile after replacing filters but shouldn't 20g be enough or is there something can check to find out why my readings are now higher?

Thanks.
 
Odd. Put the old filters back in and see what happens. Perhaps your old filters were clogged up enough that they filtered better. Do you have a baseline TDS from when you first got the unit? Is the water running faster now with the new filters?
 
Hi everyone, thanks for the replies.

I didn't flush it out, how would I do that? I did clean those 3 big containers at the bottom that hold the first 3 filters. I just used water from a hose and a brush and wiped them clean. There was some gunk in there.

I haven't recalibrated the TDS meter but it is the same one I was using before so even if it's not totally accurate it still would indicate that the reading is higher.

And it is filtering water a lot faster now with the new filters. Whereas it would take about an hour to filter 5 gallons, it takes about 45 minutes now. And the waste water is a lot less also. I save the waster water in another Brute container to use for the lawn and plants so I can tell it's less.

So flushing it seems like something to try. How would I go about doing that?

thanks.
 
What is the TDS after the RO membrane but BEFORE the DI chamber. In addition, what is your tap's TDS.

I am wondering if your RO membrane is fully seated, the last centimeter or so can be a bit difficult.
 
RO membranes have different rejection rates. The same thing happened to me last year.... went from 2 TDS to 9 TDS . Basically my new membrane was running at the minimum rejection rate of 96%.
Finally I got a SpectraPure ultra high rejection membrane which has a guaranteed rejection rate of 98% or higher.
To sum things up....you won the lottery and got a poor performing membrane...but it is within spec as most have a minimum of 96%
 
Toddrtrex said:
What is the TDS after the RO membrane but BEFORE the DI chamber. In addition, what is your tap's TDS.

I am wondering if your RO membrane is fully seated, the last centimeter or so can be a bit difficult.
Click to expand...

Ok my tap water gives a reading of 285.

After the first three filters, pre-fiter and two carbon filters, the reading is 270. Does this sound right?

After the RO membrane the reading is 14. I also took it apart again and made sure it was seated properly.

and then after the DI and that other filter, I don't know what that one is, it's 11.

I did notice this right now. I replaced the DI resin this morning and now it looks like at least half of it has already turned from green to brown! Does this sound like maybe it's bad resin?

Is a reading of 14 good after the RO membrane or could it also be that I got a bad membrane as well like advancebc29 says?

Thanks.
 
Your RO rejection rate is coming out @ 95% not that good, but your DI shoulf be able to handle 14 TDS without to much trouble. If you have another filter after the DI, try removing that and see what you get.
 
what membrane did you replace the old one with?

the color changing is just an indicator and IMO not something you should ever go by. but your DI should handle 14ppm easily. with tap of 285 you should be getting around 3ppm after the membrane depending one the type.
 
dangle said:
Ok my tap water gives a reading of 285.

After the first three filters, pre-fiter and two carbon filters, the reading is 270. Does this sound right?

After the RO membrane the reading is 14. I also took it apart again and made sure it was seated properly.

and then after the DI and that other filter, I don't know what that one is, it's 11.

I did notice this right now. I replaced the DI resin this morning and now it looks like at least half of it has already turned from green to brown! Does this sound like maybe it's bad resin?

Is a reading of 14 good after the RO membrane or could it also be that I got a bad membrane as well like advancebc29 says?

Thanks.
Click to expand...

Having your starting water at 285... you are so lucky (mine is 395 and that's still not that bad). Your 270 reading after the pre and carbon filters is about right. They are just going after the big stuff and clorine. Your 14 after the membrane is a little weak. What brand of membrane did you get? There are some out there that only reject 90%. But even at 14, your DI should clean it up. Maybe get a reading before and after that last filter (the one you don't know about). You aren't using up your resin that fast if the water out of your membrane is 14. At that level your DI should last a long time.

As a side note, I think reefers obsess over TDS readings too much. :headwally: I know cleaner is better, but it doesn't have to be zero either. My TDS runs between 5-10. But I have a friend who uses water from his well (so no clorine). It has gone thru a well filtration system (a cistern and a big DI canister) but no RO/DI system. His TDS runs between 100-125 all the time. His fish are fine, he has very little algae, he has nice zoas and LPS and even his few sps look good. He has 250w MH lights and a sump/refugium and skimmer. No DSB, no denitrator, no socks, no filter media and uses IO Reef Crystals salt. Go figure... :hmm4:
 
Hudzon said:
Your RO rejection rate is coming out @ 95% not that good, but your DI shoulf be able to handle 14 TDS without to much trouble. If you have another filter after the DI, try removing that and see what you get.
Click to expand...

a 95% rejection rate is not good. I would try a different RO membrane

The higher the TDS going into your DI the faster it will exhaust.

My recommendation is to first get a membrane that gives you 98% or higher rejection rate and move on from there. IMO anything less than 98% is throwing money away in DI resin.

The RO membrane listed in my post above will give you a minimum of 98%....well worth the few extra dollars.

good luck
 
The RO membrane I got was from Filters Direct, I always get my filters from there.

I noticed on that page that it says "it removes 95% to 98% of all chemical, dissolved solids" so it looks like I got one of the 95% ones! Sucks for me!

I also looked up what that 6th filter is, it's an "inline carbon post-filter" so I guess it doesn't do much as far as lowering the TDS reading.

Well it looks to me like it's a combination of a low performing RO membrane and DI resin. Maybe I should look elsewhere for replacements. I'll be looking at the SpectraPUre membrane and order another bag of resin and see if that helps.

Thanks for all the advice and help!
 
dangle said:
The RO membrane I got was from Filters Direct, I always get my filters from there.

I noticed on that page that it says "it removes 95% to 98% of all chemical, dissolved solids" so it looks like I got one of the 95% ones! Sucks for me!

I also looked up what that 6th filter is, it's an "inline carbon post-filter" so I guess it doesn't do much as far as lowering the TDS reading.

Well it looks to me like it's a combination of a low performing RO membrane and DI resin. Maybe I should look elsewhere for replacements. I'll be looking at the SpectraPUre membrane and order another bag of resin and see if that helps.

Thanks for all the advice and help!
Click to expand...

Why do you have an "inline carbon post-filter" ? There is no need for that, and could actually give you a higher TDS reading. I would remove it and re-test your TDS.
 
In my opinion, changing the new membrane out right now is premature.

You mentioned you have a 100 gpd membrane. 95% rejection for that membrane may be considerably OVER the factory spec. What brand of membrane are you using? You'll see membrane performance improve in the first 6 to 24 hours of run time.

How are you measuring the TDS?

What is the water pressure reaching the membrane? You may not have adequate pressure reaching the membrane.

Water general systems are in the pool of what we refer to as "e-bay specials." Given that, you have a horizontal DI, right (this is a fundamental configuration flaw)? Did you pack the DI cartridge as full as you can? It needs to be packed very tightly. The color change you are seeing may just be the result of a loosely pack DI resin bed fluidizing.

Where did you buy your resin?

Russ
 
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