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FAQs on Reverse Osmosis Device Operation

Related FAQs: RO/DI & Distilled Water 1, RO/DI & Distilled Water 2, RO/DI & Distilled Water 3, RO/DI & Distilled Water 4, RO/DI & Distilled Water 5, RO/DI & Distilled Water 6, Rationale, Selection, For Commercial/Large Output, RO Water Storage, RO Water Treatment, Maintenance/Repair, Deionizing Source Water Filtration, Kati-Ani DI Units, Kold-Steril Units, Water Changes, Water Make-up, Nitrates,

Related Articles: Water Purification Using Reverse Osmosis, Reverse Osmosis, A Multipurpose Tool By Mark E. Evans, Water Changes, Water Quality, Synthetic or Natural Seawater, Nitrates,

R/O unit; coming out of years storage      1/16/17
I stopped using my R/O / DI unit for about 3 years, I just shut off the water supply to the unit, so I assume it still has some water in it, I started it up again this week, my question is what are the issues with a unit sitting this long without use, do I need to change the membrane <Mmm; perhaps; but if it were me/mine, I'd simply test the effluent/filtered water for TDS, chlorine... even just pH. Likely if you have a carbon contactor there is no need to change out the other
and filters, what about the DI canisters, would the those be ok. I flushed the unit for 1 hour and the TDS was zero on the outgoing water.
<Oh! You're golden then. No worries>
not sure if this means its ok. is there any other tests I should do to confirm water is ok, a little confused.
thanks for your help.
Val Sammut
<Welcome. Bob Fenner>

R/o water; maint.        4/1/15
hey Bob-
I changed out all my filters on a 4 stage ro di about two weeks ago. My tds on the out put (water i collect and use) read 000.
Fast forward today, and it reads 008.
<... units?>
That's doing two thirty gallon water changes, and say another 100 in top off/quarantine filling.
Does it need to always read zero to be safe?
Realistically I can't afford 70 dollars in filters twice a month. These are fish only tanks, no coral .
How far can you let the filters go before it's unsafe?
<Depends on what the TDS, measures actually are made up of..
.. B>
My primary concern would be ammonia/chlorine or Chloramine.
Re: R/o water      4/3/15

Didn't realize tds meters varied in what they measure. They are the spectra pure tds meters, there site claims they measure the "electrical conductivity".
Sounds a bit over my head.
<Most all measure Total Dissolved Solids indirectly via conductivity. B>

new tank water, SW mixing      4/19/13
I just purchased a 265 gal tank. I have a RO system that I use to make salt water for my 50gal reef tank , but it can only make 3gal per hour. For the initial water prior to the weeks to come in cycling, do you see any harm in using tap water (bring in the garden hose) to mix with my salt? I would NEVER dream of doing that with an established tank, but a 3gal/hr it will
take a long time to fill up this tank with RO water.
<Depends on the "qualities" of your source water... See WWM re.... T'were it me/mine and there was any substantial doubt, concern, I'd just slowly fill up w/ the 3 gal./h RO... Should only take 4-5 days. Bob Fenner>

Total dissolved solids, RO     2/3/13
I have my RO system set up so that I can measure the total dissolved solids at various points in the system
The figures I currently obtain are as follows:
1) Directly after RO membrane, with tank shut off: 9 PPM
2) Directly from storage tank: 18 PPM
3) Through final polishing filter, tank shut off: 16 PPM
4) From tank through final polishing filter: 16 PPM.
This indicates that both the tank and the final polishing filter add back some impurities to the water. Is this to be expected?
Barry Blackman
<Mmm, well, zero ppm TDS is to be expected, but values in the teens aren't bad. When's the last time you switched out media? You might want to have your water tested w/ other gear. Bob Fenner>

Newbie with RO system! 4/15/12
HI guys!
<Hello Pam>
This question will be painless for you, (I hope!)
I just used my AquaFX Economy 3 Stage 100g RO System, for the first time.
It works awesome!
Question,..do I empty to <the> 2 blue chambers before I store it for next week?
<Not necessary. When you make RO water next time, just let it run for 30 seconds or so before placing the outlet tube in your container. Might want to pick up an inexpensive TDS (total dissolved solids) meter to occasionally monitor the output water quality. Very useful to indicate when the cartridges and/or membrane need replacing. Typically, RO units produce water with a TDS of 0-4 ppm.>
<You're welcome. James (Salty Dog)>

Re Newbie with RO system! 4/17/12

Oh dear, I hope you were smiling when you said that,...sorry  : /
<Oh yes, not to worry.>
Thanks for the link James!!
<You're welcome Pam.>

RO Unit... 3/28/11
I have a small RO unit (35gal) per day, for water to supply my saltwater tank. What should the PH of purified water be when it comes out? I recently put all new filters in the unit, and when I test the PH for it, its in the 7's. What should the RO water be?
<Likely somewhere in the high 6's to 7.0... to the latter w/ aeration>
<Welcome. Bob Fenner>

Water Filtration, RO gear... anomaly, trouble shooting 3/22/11
Hi folks!
Thanks so much for all your help, past and future.
<Welcome then and...>
I've been struggling with my water. Currently I have 3 (!!) RO/DI systems hooked up in my fish room, and the three of them working together only produce about 5 gallons of filtered water per day.
<By "working together" I'll assume in parallel, not series>
I started the normal way--bought one system, hooked it up. It worked for a month (10g/day even though rated @ 50gpd), then the output decreased to practically nothing. I figured I had gotten a bad system (it was really cheap), so I got a new one. The exact same thing happened with the second system. I'll spare you the details on how I ended up with the third one.
<Mmm... what is the supply side water pressure here? Many households have only about 50 psi... This low pressure translates to much less water being pushed through the RO membranes>
Things I know for sure:
1. The KH of my source water is about 25. That's the only water quality test I've done, but I think the water here (city water) is remarkably poor.
<Mmm, do see your water bill/s... contact the agency supplying, ask them to forward you an analysis of the water>
2. If I replace the RO membranes in any of the systems, I get increased flow for a few days (up to 5-10gpd though it should be 50+ according to the systems I have) then back to 1-2gpd.
<Well... there are a few other "large possibilities" here that might account for the low and diminishing RO water processing. First, do you have someone who can come and "look over" your install? Am wondering if the cartridges are arranged in order... Next, are you collecting the produced water in a non-pressurized container? I.e., just letting it flow into a car-boy, trash can or such, not a "tank" with a pressurized counter. The back pressure greatly restricts production>
3. I've tried tapping into my source water in two different ways: from a faucet and from the spigot that my washing machine uses. I'm assuming that the spigot has higher water pressure and that its water is colder, but I haven't tested this. Regardless, I don't get good flow from either source.
<Mmm, have someone w/ plumbing experience check your houses pressure (reducing valve) regulator (often inside the garage)... and if your "plumbing will take it" increase the pressure to 80-85 psi (the max. permitted in many places)>
4. I live in north Illinois. It's cold as hell here! Perhaps my source water is too cold for a RO membrane to process efficiently. I tried running a 20'0" hose from my source water thru my dump (with a couple extra heaters) to see if I could warm the source water that way. If there has been any improvement, it's negligible.
<Water temp. (unless frozen!) has little to do with this>
5. Using both hot and cold water from the faucet really isn't an option, because my hot water heater is already too small for the house and without the added load of the RO/DI system I barely have enough hot water to bathe.
<Mmm, while that plumber is out measuring your static water pressure, have them check your distal outlets... you may have an issue with the lines...>
Help! What should I do? My best idea is to try a Kold Ster-il system?
<This is a worthy tool, product of Poly-Bio-Marine, but...>
But I'm hesitant to buy one without your ok because I really don't want to own four water purification systems and still have no water. :(
Looking forward to hearing your thoughts. Thanks in advance.
<Let's chat over, investigate the possibilities mentioned above. Bob Fenner>
Re: More...re: Water Filtration 3/23/11

Thanks, Bob, for the recommendation. The plumber is my next door neighbor so I'll call him to come take a look.
<Great! That's handy>
And yes, I have been collecting my water into a non-pressurized container. Is this the kind of pressurized container that I should be looking into?
<Actually, not. You do NOT want a pressurized container... whatever non-pressurized one you're using is fine>
If so, I'll get one after the plumber comes if things still aren't going well.
Thanks much,
<Thank you, BobF>

RO\DI Systems: Warming Feed Water 7/29/2009
Hello WWM Crew,
<Hi Myk.>
As always, thank you so much for providing such a valuable resource to the hobby and to the aquarium industry. I know of no other single resource that those in the aquarium industry can rely upon for experienced and solid advice!
<Thank you for your kind words.>
My question may or may not be a simple one. I have recently moved my aquarium service company from a small farm town to a small city. Not much of a city, but the point being is that I now have to pay for water as I am not on a well anymore. Because of this I have been a little more motivated to be creative with my RO waste water and with the amount of waste water.
I am curious to see if there is a way that I could build a grid out of PVC or some other material that would allow for hot/cold to conduct through.
My idea is to place this grid in the sump of one of my coral holding systems to provide a warming of the RO feed water while at the same time cooling the reef system.
<Not a bad idea actually.>
I am assuming that the PVC is too insulated to allow for a good transfer of temp.
<Yes, a very poor conductor of heat.>
Is there another inexpensive more conductive material that would be safe for saltwater and can handle the water pressure?
<Your choices for such a heat exchanger are limited to either titanium or grade 316L stainless steel tubing, with titanium preferred. Both are resistant to saltwater and are efficient thermal conductors. That said,
they are expensive, with titanium tubing running in the neighborhood of $15.00 per foot.>
I thank you in advance for your time and look forward to hearing back from you.

Seachem Prime, SW use, and RO waste water as well 12/21/08
On my freshwater tanks i always use prime in my 24 hour aged water prior to conducting a water change.
<A good practice>
For my saltwater tanks i also use prime prior to mixing my salt for partial water change. I now have a RO filtration system fitted, and would like to know if i need to continue to use the prime.
<Mmm, not necessary. For browsers, this product desc.:
I have started to use the RO water for drinking and for topping up my sump. Can i continue to use my tap water plus prime for my partial water change on my salt water tanks, or is it best to use the RO water.
<Mmm, really depends on the nature/constituency of your source/tap water...
and your goals in using the RO... but if using tap, I would use the Prime>
It seems to be a very slow process waiting for the trash can to fill with RO water, and the waste involved is very high.
<Mmmm, I would think about ways to use the vented "solute water"... I have run out to my pond before and/or to a cistern to in turn water my garden.
There's really not "that much" different than the tap... so, you might very well be able to simply collect this "waste water" and use in on your freshwater systems. Bob Fenner>

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