RO/DI Filter Changing Questions!!

JoeMomma · #1 12/30/2007, 05:17 PM

I read the TDS of my RO/DI water a couple weeks ago and it was at a few ppm. I decided to change the first 2 stages (sediment and choline) as a precaution because I didn't want to damage the more expensive RO and DI parts.

I just measures TDS and now I have a reading of 8 ppm. What have I done wrong and what can I do to prevent from making more mistakes?

Thanks.

coope81 · #2 12/30/2007, 05:30 PM

Did you rinse you carbon filter in RO before you put it back in, small particals can be relesed from this and damage your membrane and this could be your problem. I know cus i did this!

JoeMomma · #3 12/30/2007, 05:42 PM

I did not do that!!! Is it too late to bother now????

coope81 · #4 12/30/2007, 05:57 PM

Make sure you test your fresh RO in a clean glass not! you usual container or salt mixing bucket even dust can give you a high reading.
If its still the same you can try rinsing your carbon filter and giving your membrane a flush if your RO unit has that function on it.
Then you could try running it for 3 or 4 hours and then see what its like.
If that dont work take all filters out inc membrane and flush it, check for any visible membrane damage then rinse all filters again in RO, be sure not to let membrane dry out.
Good Luck.

JoeMomma · #5 12/30/2007, 06:04 PM

Thanks coope! I don't have a flush function on my RO/DI unit. I guess I'll have to manully remove and rinse.

AZDesertRat · #6 12/30/2007, 06:24 PM

Prefilters and carbons have almost no effect on final TDS, that is strictly the job of the RO membrane and the DI resin.
If you bought a good quality carbon block its not that big a deal if you did not flush it. In the future though, when installing new filters, disconnect the line from the carbon block up to the membrane at the membrane end and flush it to waste for a minute or two to remove any carbon dust. You probably won't see much unless you are using either a cheap carbon block or granular activated carbon, both of which you should not be using.
To test the TDS, first get your self a nice squeaky clean drinking water glass with absolutely no water spots of soap residue. Fill it with tap water, stick the TDS meter in it and allow it to stabilize. Record the reading. Next, and this is very important, triple rinse the glass and meter in DI water. Always do this between tests and upon completion so the glass and meter stay clean.
Next fill the glass with RO only water and again let the meter stabilize. Triple rinse again with DI and finally fill the glass with RO/DI water and take a final reading. Rinse both the glass and meter and put them away clean.
You should be seeing a 95-98% reduction in TDS from the tap water with the RO only. So for example if your tap TDS is 200 you should see no more than 10 and hopefully about 4 with RO only. After the RO/DI you should be seeing 0 TDS or very close to it. When youy begin to see any TDS other than a steady 0, its time to change the DI resin. Change the prefilter and carbon every 6 months like clockwork and always use quality filters not e-bay specials. These two filters are what will make your RO membrane last and work well.

Don't worry about rinsing it now, its already passed the fines if any.

JoeMomma · #7 12/30/2007, 07:06 PM

So then as time passes I should see a reduction in my TDS as what I'm reading now is what wasn't intially rinsed. I've probably made 40-50 gallons of water since I changed the filters.

If my negative readings persist should I be changing both RO and DI? As stated above, when TDS is not a steady 0 I should change the DI resin but my RO membrane may be been damaged as since I didn't rince the carbon...

Thanks again for the great help coope and desertrat!

AZDesertRat · #8 12/30/2007, 07:27 PM

Its not going to get any lower. Filters should rinse up after just a few gallons at most.

You did not damage anything.

Test your Tap Water TDS, RO only TDS and RO/DI TDS and post the numbers. You need all three to troubleshoot the system.

coope81 · #9 12/30/2007, 07:42 PM

First make sure your TDS meter is calibrated.
If you have used a clean glass to test in and its still the same you could try as instructed above and have a good look at your membrane just to make sure?
It sometimes helps to start over from the beginning making sure all is clean and flushed just for self reassurence.
If all fails i would change your DI resin first as its cheaper if you still have no luck change your membrane.
I know it a pain cus i've been there myself, Good Luck.

JoeMomma · #10 12/30/2007, 07:48 PM

Ok going to try the 3 tests and see what I come up with...

JoeMomma · #11 12/30/2007, 08:07 PM

Tap: 82 ppm
RO: 1 ppm
RO/DI: 0 ppm

Looks like the higher TDS in my storage container was from the crud that had come off the carbon filter. All seems good to go for now! I hope.

Reefcentral (and its members) does it again!

coope81 · #12 12/30/2007, 08:19 PM

It was almost certainly the crud what was already in there I'd say.
just be carful what container you use to test in and keep lids on stored RO/DI water as this is going in your tank and even if your RO/DI is 0 tds your container might be contaminated, keep them well rinsed.
Glad its sorted

AZDesertRat · #13 12/30/2007, 08:40 PM

Always test directly from the unit. Storage vessels can build up slime coats. RO/DI water is very agressive and is constantly trying to attract things to get back to its natural "dirty" state. Even left alone in a perfectly clean glass it will attarct things out of the air and start to show TDS readings in just a short time.