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Fishingpcola
10/15/2009, 07:53 PM
I have a dual inline TDS meter on my RODI. I test water in and out of DI. I just changed the filters 2 months a go. My meter is test 24 ppm in and 12ppm out of the DI. Is 24 ppm in to DI acceptable and my DI just needs replacing? Visably the DI is 1/2 color changed or does the membrane need to be changed? I plan on test water with another source to verify the TDS.
Thanks

preef
10/15/2009, 08:35 PM
What is the TDS system into the RO. If it is really high then 24 ppm may be all yo can expect. 12 ppm out of the DI sounds really high. That should be 0. IME the DI needs to be replaced well before it is completely color changed.

kgross
10/15/2009, 09:34 PM
With a good membrane, 24 tds out, should mean you have around 480 tds going into the membrane (95% rejection). But depending on the membrane you could have as low as a 90% rejection.

So to really answer your question we need to know the TDS of your TAP water, and what membrane you have.

With that said 12 TDS out of your DI is not good, but only have 1/2 visible exhaustion is not surprising, Some ions are weakly held, and will be replaced by ones that have a stronger bond, on my area silicates go through a 1/2 exhausted DI.

This is one reason I suggest running dual DI units. When the first one show complete exhaustion, replace it, and move the 2nd one to the first place (and normally it will show around 1/4 exhaustion, and put the new in the back. That way you have the extra unit to still try and remove the weekly held ions.

Kim

bertoni
10/16/2009, 12:04 AM
I don't think 12 TDS is a very good result, as has been stated. Once we know the tapwater TDS, we likely can help more.

Buckeye Hydro
10/16/2009, 04:09 AM
kgross and bertoni are right on the money. Good posts!

Assuming your tds readings are right, we know your DI resin needs to be replaced, but we can't say w/o more info if your membrane is OK.

Also - let us know the pressure at the membrane (after the prefilters).

Russ

Randy Holmes-Farley
10/16/2009, 04:55 AM
FWIW, I address some of these issues here:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

Fishingpcola
10/16/2009, 08:03 AM
Thanks. I'll test water into the RO tonight. I went ahead and ordered both membrane and DI from BRS. Unforunately I am having to do a water change tomorrow. When the new DI comes in I will perform more water changes and run gfo.

Fishingpcola
10/16/2009, 05:50 PM
Tap water is 70. So I should change out membrane and DI.

kgross
10/16/2009, 07:21 PM
If your tap water is only 70 and you are only getting down to 24, you have a problem, either a bad membrane, or the membrane is not setted correctly. First I would suggest opening up the membrane housing and making sure it is seated correctly, check again, and if it is not better, get a new good membrane. Dow filmtec 50 to 75 gpd membranes are very good.

Kim

Fishingpcola
10/16/2009, 07:52 PM
Thanks Kim! It might have happened last time I had to pull the unit out to change the filters.

Billybeau1
10/18/2009, 04:26 PM
FWIW, membranes should last a long time. Especially with your tap tds. Some have been known to last over 6 years.

I'm with Kim. Your membrane is not seated properly. With a tap water tds of 70 ppm, you should be getting 3 to zero out of your membrane. The di polishes the rest.

You haven't mentioned what brand ro/di unit you have. :)

Fishingpcola
10/18/2009, 04:45 PM
RODI was purchase from melevreef. Filters were just replaced from BRS. I just ordered a new membrane and DI from BRS.

Billybeau1
10/18/2009, 05:11 PM
I would re-seat your membrane per the instructions and check again. Unless your unit is over five years old, I doubt your membrane is exhausted.

I'm not familiar with melevreef ro/di units but I know my membrane can be pushed in too far rendering it useless.

I suggest you contact the manufacturer and get their advice. Membranes are not cheap and one should last for years. Sometimes 6 to 8 years.

Just trying to save you some bucks. :)

Fishingpcola
10/18/2009, 06:11 PM
It is only one year old.

bertoni
10/19/2009, 12:28 PM
I'm guessing it's a seating problem, but it could be a defective membrane.

am3gross
10/19/2009, 12:34 PM
some good info here that i did not know!

Buckeye Hydro
10/19/2009, 12:47 PM
Check your waste water to purified water ratio. Line up 6 to 8 identical glasses in front of the system. With your waste water tube in one hand, and your DI tube in the other, how many glasses do you fill up with waste water in the time it takes you to fill up one glass with DI water?

If you have a membrane that isn't seated, that ratio will be low.

If the ratio is low and the membrane is fully seated, and you don't think the ratio being off is caused by other issues, another thing we see occasionally that the little "cup" into which the membrane seats develops a crack or chip.

Russ

Fishingpcola
10/20/2009, 06:49 AM
Thanks, I'll try this. How often do tds meters go bad. The reason I asked is last night when I checked the water out of the DI it recorded 56ppm. This morning it tested 14ppm. Both measurements were taken with the ball value closed. My reservoir is full so I do not need to produce.

njdevilsfan
10/20/2009, 08:06 AM
i have a melevs rodi
my tds out of the tap is in the 700s
i am still on my first membrane
and my unit is over 2 years old
your must be seated wrong

bertoni
10/20/2009, 12:13 PM
Hmm, I suppose it's possible the TDS meter is bad. I would get a calibration fluid to check it.

Billybeau1
10/20/2009, 12:56 PM
Thanks, I'll try this. How often do tds meters go bad. The reason I asked is last night when I checked the water out of the DI it recorded 56ppm. This morning it tested 14ppm. Both measurements were taken with the ball value closed. My reservoir is full so I do not need to produce.

The in-lines need water flowing past the sensor. It will not read right if water is not flowing.

Fishingpcola
10/20/2009, 01:18 PM
The in-lines need water flowing past the sensor. It will not read right if water is not flowing.

Thanks, this is good to know. I plan on dumping some water to enable flow to check tds.

Waterobert
10/20/2009, 01:22 PM
I have 550 going into RO/DI unit, 8-9 comming out of RO membrane and 0 out of DI. Something is not right with your RO/DI unit.

Fishingpcola
10/20/2009, 02:30 PM
The in-lines need water flowing past the sensor. It will not read right if water is not flowing.

Is it possible to use an in-line to test tap water by placing tab water in a tub with a powerhead blowing water past the sensors?

Billybeau1
10/20/2009, 02:44 PM
Where do you currently have your 2 meters set on the ro/di ?

bertoni
10/20/2009, 03:31 PM
The TDS meter should work in the bath tub as long as there aren't any air bubbles inside the mechanism. I wouldn't use the powerhead: it might cause more problems than it solves.

njdevilsfan
10/20/2009, 04:41 PM
why not pm melev he is good at all things rodi wise

Buckeye Hydro
10/20/2009, 07:01 PM
Is it possible to use an in-line to test tap water by placing tab water in a tub with a powerhead blowing water past the sensors?


Wow - that sounds like a lot of work for something you'll likely want to check periodically. You can get a good handheld HM Digital meter for less then $20...

Russ

Fishingpcola
10/20/2009, 07:20 PM
24" before DI and 24" after DI. I have water flowing going for 5 minutes now and out of DI reads 20ppm and 18ppm into DI. How can my DI be adding to my tds?

Billybeau1
10/20/2009, 07:32 PM
I know we've covered this before but did you try reseating your membrane or did I miss it somewhere ?

With your tap tds, you should be getting much lower tds post membrane.

Fishingpcola
10/20/2009, 07:48 PM
Here is a new one. I turned the water off at the tap. Pulled both sensors to make sure they were in correctly. Turned water back on. In the DI "ERR" out of DI 231ppm.

Billybeau1
10/20/2009, 08:24 PM
You may have put them on backwards. The is an orientation to those sensors. Look real close.

Also try shutting the unit off and turning it back on again.

Fishingpcola
10/20/2009, 08:38 PM
The instructions say make sure the flow runs between the two probes not along. They do not indicate a direction (front and back). I plan on calling BRS tomorrow. The meter is maybe 6 months old.

Buckeye Hydro
10/21/2009, 04:54 AM
the resin, when exhausted, WILL add tds back into the water and your DI numbers will be higher than your RO numbers.

Feel free to give us a call when you are in front of the system if you'd like help troubleshooting.

Russ

Fishingpcola
10/21/2009, 10:46 AM
Thanks Russ! What are the hours that I may call between and which number should I call?

Buckeye Hydro
10/21/2009, 02:23 PM
You've got a PM...

Russ

Fishingpcola
10/21/2009, 06:41 PM
Ok. I changed out the DI and pulled out the membrane and reset it. I am running a few gallons into a bucket and will test afterwards.

Fishingpcola
10/21/2009, 06:55 PM
I pulled the water line into a 5 gallon bucket and the DI out line into a 3 gallon bucket. Here is the part that makes me feel stupid. Several months ago when I installed the inline tds meter I placed a small ball value on the line out of the DI to shut the flow into my resevior. This only prevents water from flowing into the resevior not from flowing through the membrane. So for the past several months I have been running water through the membrane 24/7 thus the membrane is spent!

bertoni
10/21/2009, 11:11 PM
Ouch! Okay, I can see that a membrane might fail under that load.

Randy Holmes-Farley
10/22/2009, 04:57 AM
I have water flowing going for 5 minutes now and out of DI reads 20ppm and 18ppm into DI. How can my DI be adding to my tds?


Those numbers are well within experimental error, but yes, TDS can rise coming out of an exhausted or partially exhausted DI resin. You simply swap a less conductive ion going in for a more conductive ion coming out.

Fishingpcola
10/22/2009, 06:12 AM
So last night I replaced the membrane and the DI. I ran the system for 1 1/2 hours into a 5 gallon bucket and discarded. I hooked up the line to the resevior and filled up over night. This morning as water was still running the tds were 25ppm into the DI and 23ppm out of DI. Could the meter be that far off from calibration? I would expect the variance to be 1-3ppm difference. I did reposition the ball valve before the RODI. I expect my water bill to go down now!

Randy Holmes-Farley
10/22/2009, 06:37 AM
I expect the DI is depleted, and there is no reason to suspect problems with the meter that I can see.

Fishingpcola
10/22/2009, 07:33 AM
I expect the DI is depleted, and there is no reason to suspect problems with the meter that I can see.

Randy, you misread. I replace with a new membrane and new DI and the unit is at 23ppm.

Randy Holmes-Farley
10/22/2009, 07:40 AM
Does it read 23 ppm TDS in air?

"Calibration" is not generally an issue for reading 0 ppm TDS. It may be broken and stuck at 23, but zero is zero. It is only the slope that changes with calibration. If it reads 0 ppm TDS in air, then there is a good chance the DI is depleted or somehow water is getting through it untreated, whether it is new or not.

Is the DI horizontal by any chance?

Fishingpcola
10/22/2009, 08:03 AM
Vertical. I replaced it last night with DI from BRS.

tmz
10/22/2009, 09:41 AM
I use an in line meter between the two di cartridges and a portable hand held meter to check other outputs. Works for me.

Fishingpcola
10/22/2009, 12:08 PM
I found a local store with a tds meter. I will verify tomorrow.

Randy Holmes-Farley
10/22/2009, 12:18 PM
Did you try it in air?

Were the most recent values in line? When not measuring inline, a little, tiny, tiny bit of contamination in the collecting container can drive up the TDS.

Fishingpcola
10/22/2009, 02:09 PM
No I have not tried it in the air. What should an air rate give?

Randy Holmes-Farley
10/22/2009, 02:29 PM
Always 0 ppm TDS. :)

Fishingpcola
10/22/2009, 05:28 PM
I have pulled the sensors out and dried them off with a paper towel and the numbers are either in the 30's or 40's depending which sensor you are looking at. I called HM Digital and they told me should be zero and to send it in.
Thanks Randy.

Randy Holmes-Farley
10/22/2009, 05:29 PM
:thumbsup:

Sounds like a good plan.

Good luck. :)

Fishingpcola
10/22/2009, 06:37 PM
Now I need to repair the auto shutoff valve. Never ends!