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JTL
10/12/2012, 01:08 PM
My tap water is about 200 TDS and my RO is 129 but after running my RO through DI it is 329! I changed it about 100 gallons ago and it was barely measurable. One thing I have noticed is that it doesn't last very long but this is a new issue. Any thoughts on what is causing it?

disc1
10/12/2012, 01:11 PM
If you're putting 129ppm TDS through the DI stage then yeah it's going to burn up real fast.

You've got 200 out of the tap and 129 out of the RO. Something is BAD wrong. You've got less than 50% rejection there. Let's look at the RO membrane first.

JTL
10/12/2012, 01:18 PM
I replaced the membrane a few months ago. Maybe 1500 gallons of use. I periodically backflush it.

spinsonic
10/12/2012, 01:27 PM
did you flush the unit for at least 5-10m before making water? I notice my tds waste water reading is 120 when first on, then gradually drops down to 9.

JTL
10/12/2012, 01:29 PM
Yes, because I was making some make up water when I decided to test it.

hkgar
10/12/2012, 01:30 PM
Do you have a sediment and carbon filter on your setup?

JTL
10/12/2012, 01:30 PM
Yes, both of them.

disc1
10/12/2012, 01:32 PM
I replaced the membrane a few months ago. Maybe 1500 gallons of use. I periodically backflush it.

First time you checked it since you changed the membrane?

My first suspect would be that the membrane isn't seated well or is leaking water past it for some reason.

hkgar
10/12/2012, 01:42 PM
How often do you change the Sed And Carbon filters?

Psyops
10/12/2012, 01:45 PM
If it's possible trying a different membrane. I had a bad membrane years ago. I did not have a reef tank at that time. It was just a 10 gpd membrane.

Alex

JTL
10/12/2012, 01:46 PM
Yes, I didn't check it when I put it in so I have no point of reference. I think it is seat fine but if there is a bad seal then that could be the problem. I got this replacement from Pure Water Club which does not have the best reputation even though it was supposed to be American made and looked exactly like more expense ones. May be a rip off.

Mavrk
10/12/2012, 01:48 PM
The first 2 stages do not affect TDS, but can kill a membrane faster if not changed. I suspect the membrane is not seated correctly or is defective. What is your pressure? What is the waste:RO ratio? What are you using to measure TDS? Are you measuring the water directly after the DI or from the holding container? If the latter, dust and the like can raise TDS readings. But if you are getting anything higher than 8 directly from the membrane, then something is wrong with the membrane and you should not run it to the DI. Also, what RO/DI unit are you using?

JTL
10/12/2012, 01:48 PM
How often do you change the Sed And Carbon filters?

I has been a while but the sed doesn't look too bad.

Mavrk
10/12/2012, 01:50 PM
Yes, I didn't check it when I put it in so I have no point of reference. I think it is seat fine but if there is a bad seal then that could be the problem. I got this replacement from Pure Water Club which does not have the best reputation even though it was supposed to be American made and looked exactly like more expense ones. May be a rip off.

I would try opening it up and try pushing it in further (with a little twist) using a pair of pliers. Then see what happens.

JTL
10/12/2012, 01:53 PM
[QUOTE=Mavrk;20778046]The first 2 stages do not affect TDS, but can kill a membrane faster if not changed. I suspect the membrane is not seated correctly or is defective. What is your pressure? What is the waste:RO ratio? What are you using to measure TDS? Are you measuring the water directly after the DI or from the holding container? If the latter, dust and the like can raise TDS readings. But if you are getting anything higher than 8 directly from the membrane, then something is wrong with the membrane and you should not run it to the DI. Also, what RO/DI unit are you using?[/QUOTE

Pressure is 55 psi
Unit is from Pure Water Club as are the carts
I measured the water directly from the DI

Probably a crappy membrane.

tekjunkie28
10/12/2012, 02:02 PM
Here is a tip for everyone here. Run your RO water for another 2 to 5 minutes before you connect it up to the DI and it will save you lots of resin. I have a inline connect that I just take the hose out of and run it and check TDS before I hook it back into the DI. One thing though, how often should I flush the RO membrane?

JTL
10/12/2012, 02:25 PM
I still don't understand how running water through the DI can increase the TDS from what is coming out of the RO pre-DI. Should be equal to or less in my mind.

Mavrk
10/12/2012, 02:27 PM
I still don't understand how running water through the DI can increase the TDS from what is coming out of the RO pre-DI. Should be equal to or less in my mind.

The DI could be leaching out the adsorbed TDS.

JTL
10/12/2012, 02:35 PM
Not sure how, that part of the unit I purchased from BRS and it worked in the past.

disc1
10/12/2012, 03:01 PM
I still don't understand how running water through the DI can increase the TDS from what is coming out of the RO pre-DI. Should be equal to or less in my mind.


It's because of the way the TDS meter works. It is actually measuring conductivity and then doing a conversion. Well, not all ions affect conductivity in the same way. So the number it gives you is a conversion based on a certain species (NaCl usually I think). If your DI is exchanging soft ions for harder ones, then the ions coming off may have a greater effect on the conductivity and therefore the meter reads higher even though the total number of ions is the same or even less.

TDS meters are NOT an exact science.

disc1
10/12/2012, 03:07 PM
The DI could be leaching out the adsorbed TDS.

Not sure how, that part of the unit I purchased from BRS and it worked in the past.

Sure it worked in the past before it was exhausted.

DI resin starts off with acidic and basic groups on it H+ and OH-. It exchanges those for other ions in the water and the acid and base get together to make water. So you get pure water out.

Now you have replaced all those acidic and basic groups with other things. So the DI resin is exchanging those things for which it has lower affinity (phosphate, silicate, other "soft" ions) for those things for which it has a higher affinity (sodium, calcium, chloride, "hard" ions) by the same process.

If it becomes full enough, it can even release those softer ions into pure water. Usually they will get trapped again a little further through the resin, but your resin is burned up now so they just pass right on through.

JTL
10/12/2012, 05:17 PM
I suppose I need to change out the membrane and check the results. It is an Axeon if that means anything.

disc1
10/12/2012, 05:24 PM
Make sure it is seated good and not leaking past it before you spend money on a new one.

JTL
10/12/2012, 05:35 PM
Thanks, I did take it out and re-seated it but I don't know if it will make a difference. Cannot tell if the seal is good, although it looks like it is.

Buckeye Hydro
10/14/2012, 09:41 AM
Good advice in this thread.

One other thing people didn't mention - make sure you are letting the system run for 2-3 minutes before you test the TDS of the RO water. You'll get a pulse of not-so-clean water from the membrane when you first turn the system on.

Russ

JTL
10/14/2012, 09:49 AM
I think I have tried everything and from what I can tell the membrane is no good. Thanks for all of the advice.

bertoni
10/14/2012, 04:29 PM
You're welcome! Sorry about the membrane!

JTL
10/15/2012, 01:57 PM
As I was going to order a new membrane and pre-filters a couple of things occured to me. I read somewhere that the flow restrictor can go bad, is that true? If so I better get a new one. Also I seem to have a lot of "stuff" on my RO. I have a sediment filter and (2) carbon block filters and some type of finishing filter for drinking water, in addition of course to my DI filter. Seems like overkill. I also have an auto shut off device which I wonder if is really necessary. Any opinions on this?

Buckeye Hydro
10/15/2012, 02:34 PM
Two carbon blocks generally not needed unless you have chloramines.

Finishing taste and odor filter not needed except between a pressurized tank and a faucet.

ASOV needed only if you want the system to shut itself off.

JTL
10/15/2012, 02:41 PM
I have a pressurized tank and a drinking faucet, I also have a by-pass for the drinking water to not be de-ionized for what that is worth. Help me with this. If I don't have an auto shut off will the system keep running water even if the I am not using any? Seems like the tank would fill and that would be it unless there is a by-pass.

bertoni
10/15/2012, 05:15 PM
Flow restrictors shouldn't go bad. I don't know what that means. As long as the retrictor matches the membrane, the filter will be fine.

I'm sorry, but I can't answer the question about the drinking water setup. I would the that the filter would fill the tank until the air pressure matches the water pressure, but I don't know exactly how such setups are plumbed.

JTL
10/15/2012, 05:51 PM
I just wonder if most of these units have a shutoff valve or if I have more junk than I need. I don't have a clue about the flow restricter or if anyone has ever had to replace one. In theory, I suppose they could get clogged up and create more resistence.

Buckeye Hydro
10/17/2012, 08:41 AM
JTL - there are concerns with drinking water systems that also produce DI water - there are lots of ways for them to be mis-plumbed (many are). Do you want to give us a call?

Russ
513-312-2343

JTL
10/17/2012, 08:50 AM
Russ,
I am just going to take out the pressure tank and I believe I can also remove the auto shut off device as well. We really don't use this unit much for drinking water so I am not too concerned about stripping the minerals out of the water from a health standpoint. My goal is to make this system as simple as possible, remove the pressure tank, auto shut off, post filter and one of the two carbon block filters. Thank you for your thoughts.

JTL
10/20/2012, 04:09 PM
Update. I replaced the membrane, the filters and the DI and the water is 7 after the RO and 0 after the DI. However, I cannot figure out why my house pressure is 60 psi at the tap next to my RO unit but only showing 45 psi going into the housing (this is after new filters). I wonder if the 1/4" tubing is restricting the pressure that much, if so maybe I could try 3/8". I may also just put the gauge at the end of the tubing before it goes into the pre-filters and see what I get. Anyone else seeing this much of a drop?

bertoni
10/20/2012, 04:42 PM
Are you measuring after the carbon and sediment filters of your RO/DI unit? I'd expect a drop across them, although I have no idea how much the drop should be. Or do you have some other filters before the standard RO/DI prefilters?

JTL
10/20/2012, 05:19 PM
Jonathan, yes after the filters just a sediment and carbon, but they are brand new so I was surprised at at 15 psi difference.

bertoni
10/21/2012, 12:47 AM
I'm not sure how much you should lose, so I wouldn't worry yet. What is the TDS at the tap?

Buckeye Hydro
10/21/2012, 04:07 AM
What is the length of the 1/4" tube feeding the system?

JTL
10/21/2012, 06:57 AM
TDS at the tap is about 200 and the tube length is about 4'. This is probably not a big deal but it would be nice to get the max pressure possible. I am going to put the gauge at the end of the tube before it goes into the pre-filters and check the pressure. That should tell me how much the line tap and the tube are restricting the flow.

Buckeye Hydro
10/21/2012, 07:23 AM
4' of 1/4" tube is negligible.

tmz
10/21/2012, 09:06 AM
When I 've had trouble with high tds in the ro water ;it was from a crumpled seal on the membrane ,allowing unfiltered water to passrigh trough. It's the frist thing I'd check.

JTL
10/21/2012, 09:36 AM
I replace all of the pre-filters and the membrane so now my tds is zero. I am trying to figure out why the pressure in the pipe is 60 psi and the pressure in the supply to the RO is only 50 psi. I am thinking it is the restriction of the 1/4" fitting and tubing.

Buckeye Hydro
10/21/2012, 09:38 AM
Nope. Could it be the difference in readings on two low cost gauges?

What is the gpd of your membrane?

JTL
10/21/2012, 09:39 AM
75gpd

Buckeye Hydro
10/21/2012, 09:51 AM
Then no, 1/4" housings and 4 feet of feedwater tube is not your issue.

Russ

JTL
10/21/2012, 10:13 AM
Like I said probably not anything to be concerned about other than a curiosity issue. I would be interested to know how much loss others have experienced if anyone has even checked. Most probably just look at the pressure going into the membrane and if it is sufficient that is enough info.

bertoni
10/21/2012, 05:01 PM
Your membrane is running at 96.5% rejection or so, which isn't all that bad. There might be a bit of a sealing issue, or maybe those filters are taking a bit too much pressure out of the system. I don't know enough to help more, but 98% is about all you should expect for rejection.

JTL
10/21/2012, 05:06 PM
Thanks, it is good enough for me considering that the tds has been 180 for who knows how long. The corals and fish are doing good and that is the most important part.