Typical PH for RO water

[emilio50]

At what PH is your RO water. Mine comes out at around 7 ppm, but at a PH of around 7.6


Does that seem normal?

[KDodds]

A pH of 7.6 is quite high for RO water unless it started out high and your not circulating it. Using an airstone or powerhead will get you closer to neutral, usually, within 24 hours. 0ppm TDS RO water will usually be very slightly acidic.

[MostlyDiscus]

6.8 or 6.9 for me

[Don Trinko]

I read that it is difficult to test ph of ro with normal kits because the chemicals used to test it will effect the ph. Don t.

[Graham]

There is an interaction with CO2, CO3, HCO3 and pH in water H2O

If your water has high CO2 going in and since it's a gas and not removed by RO mambranes, it may react with the water to form bicarbonates.........buffering chemistry:bandana: anyway it wouldn't be impossible for the pH to be higher.

G

[KDodds]

I read that it is difficult to test ph of ro with normal kits because the chemicals used to test it will effect the ph. Don t.

Some kist are more accurate than others. I try to compare kits to my probe when I can (probe is used for 450 SW pH controller, real time). I've found that with most popular brands, you'll get a fair enough accuracy, and more importantly, a consistent one, to be reasonably assured of being where you want to be. In this respect, where an exact target number is not as important as consistency of test results, if you have a lot of tanks, or use a lot of water for changes, the dip strips are actually the easiest and quickest method and are reasonably accurate.

[Don Trinko]

IMO; I'm thinking that since you can not use pure ro it's ph doesn't mater much because whatever you add to it to make it suitable for discus will determin the ultimate ph. Don T.

[FLGirl1977]

Mine comes out at a straight 6. I even add Ken's RO right to stabilize the pH for when it goes into my tank at 100 PPM, and still doesn't go above a 6. I just made a post about this...

[KDodds]

Are you aerating in some fashion (airstone, powerhead) before using it? It may just be that the buffer just happens to buffer at 6.0, or, you may have a faulty pH test kit.

[FLGirl1977]

Not sure if you were asking me, but yes... I have the RO water in a large rubber garbage container with a pump circulating, a Korelia powerhead for aeration and the water is also heating to 84 F...

I use a Tetratest Laborett drip test kit...

[KDodds]

You might want to verify your results against anohter test kit (or bring to your LFS), just to be sure. What is the TDS level of your RO product water?

[FLGirl1977]

TDS= 100 ppm (after adding RO right)

[KDodds]

What about before adding anything?

[FLGirl1977]

What about before adding anything?

I just went to go test it and my battery died on my TDS meter... lol. Going to get a new one today and test it. :o

[KDodds]

Isn't that always the way? LOL. My thinking is that the product water coming out of your RO unit may already be buffered to some degree that is not being change by the minerals/elements you're adding. Are you using a softener? Prior to the RO unit?

[emilio50]

In my case, the RO water used to come out at a PH of about 4.5. Now it is coming out at around 7.6

My original theory was that the membrane was not working properly. However, I now have a new membrane and it is still coming out at 7.6 I also calibrated my PH meter and it was OK.

Am I to conclude that something in the input water has changed.. maybe because of the season?

[KDodds]

MANY local water supplies have seasonal changes in water quality and parameters. In fact, I know of a few folk out west near Portland who had some REALLY bad problems maybe 2 years ago with agricultural run off. RO units, though, should not produce water with a pH of 4.5. That's extraordinarily low for pure water. It's possible some trace remained that drove the water that acidic, I guess. As for the 7.6, if you aerate the water overnight AND you RO unit is functioning properly, it should come out much closer to 7, usually a bit under.

[FLGirl1977]

Got the TDS meter working and BEFORE we add the RO right it was an 8 (but that could be the bit of residual water from the last water change where the minerals were added.

[KDodds]

8ppm and it still comes out to a pH of 6 after aeration for 24 hours?

If this is the case, and this is not as uncommon as you might think, your ambient CO2 levels in your home might be quite high. CO2 levels rising in the winter in homes is pretty common. To the extent that it would push your pH down to 6, though, isn't that common. But, it is a possible reason. You might try aerating in a ventilated room to see if it makes a difference. While 6.0 is fine, great even, for discus, and can see where you'd want to figure out the whys of your RO product water.

[FLGirl1977]

Not sure if this makes a difference, but the rubber garbage can that we store the water in has a lid on it (but cracked because of the power cords from the pump, heater and powerhead). I keep that lid on to ensure no harmful chemicals get into the water while it's sitting. Where we live in FL, I'm not sure that the CO2 levels are that high. Even when it's cold out we have the house open and well ventilated... although I could be wrong, but I just don't see it being a CO2 issue. I'm curious to hear your thoughts though...

Keep in mind though that the water that's going through the RO unit is 'reclaimed water' which is one step away from drinking water here, just not chlorinated... not sure if that would affect anything.

[Patr1ck]

My ph is about 6 and goes to about 6.5 after adding ro right to ppm of 130. I use the Hanna instruments combo tester and calibrate it before I take any readings also.

P

[KDodds]

Could very well be because the can is covered. Unless there's a problem, though, I really wouldn't worry about it, particularly since, after it's mixed up with a reconstituting agent and in tank it's pretty darn near, if not, perfect. ;)

[pcsb23]

I think that when it comes to measuring the ph of RO water there are several factors to take into account.

The first is that there is very little mineral content so any electronic meter, particularly the pen types, is likely to struggle to read it accurately. I wrote to Hannah instruments a while back seeking clarification as to how accurate these meters are. I got an interesting response which I've copied below for completeness. It indicates that in order to get a true reading below 70 microsiemens a special probe is needed and that this probe needs to be looked after carefully....

And although it has been a long time since I did chemistry, in particular gaseous exchange between water and the atmosphere, I cannot believe that the ambient levels of CO2 in a room could have any significant effect on ph, no matter how little mineral content there be in the water. There is 0.033% CO2 in the atmosphere, given the rather large volume of the atmosphere it would take a significant amount to radically alter this.

Response from hannah instruments - note they tested other manufacturers probes.

WATER QUALITY--Electrodes for pH measurement in low-conductivity waters

In Reply Refer To: February 10, 1981
EGS-Mail Stop 412

QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 81.08

Subject: WATER QUALITY--Electrodes for pH measurement in
low-conductivity waters

As pointed out in Quality of Water Branch Technical Memorandum
80.19, the procedures and equipment needed to obtain an accurate
pH value are more exacting for samples with very low specific
conductances than for samples with higher specific conductances.
At specific conductances below about 70 mhos, many instrument-
electrode systems give erroneous readings. Recent tests with
several different pH electrodes and instruments, and evaluations
of their precision when used to measure pH in low-conductivity
waters, have suggested that the electrode is the critical
component.

Many manufacturers are now supplying electrodes designed for low
conductivity waters. Some electrodes not so designed seem to work
well also. Following is a list of electrodes that have been either
claimed by the manufacturer to work well in low conductivity
waters or tested by personnel in the Division and found to work
well.

Corning Glass Works 476182 * Plastic barrel

476223 Semi-micro, combination glass

Orion Research 91-62 * combination glass with
KCl/KN03 solution

Sargent-Welch S-30072-15 * General purpose electrode

Leeds ~ Northrup 117493 Meredian, KCl gel combination

* Tested by Division personnel.

Any instrument used must have slope compensation and temperature
compensation, and be accurate to at least 0.05 pH units. Although
most general-purpose portable pH meters are suitable, the better
grade meters usually provide a more stable measurement.

Electrodes designed for low-conductlvity waters are not as
resistant to physical shock or exposure to strong chemicals as are
the electrodes customarily used in the field and can be easily
damaged by improper treatment. To protect the electrodes follow
these guidelines in addition to the procedures given in Memo
80.19:

l) store the electrodes in deionized water or covered with a cap
containing deionized water; do not use KCl solution or buffer for
storage; 2) do not expose the electrodes to strongly acidic or
alkaline solution, or to very high-conductivity waters; 3)
restrict use of the electrodes to waters with conductivities less
than 200 umhos.

You will recognize that the buffers used for calibration are high-
conductivity solutions. Use of buffers for calibration is the
single exception to the guidelines. Efforts are continuing to
develop suitable standards in dilute acids for use in the field.

We advise offices that are or may be making pH measurements in
low-conductivity waters such as precipitation to select their
equipment carefully, then dedicate it solely for this purpose. By
so doing, much time will be saved and more reliable results will
be obtained.



R. J. Pickering
Chief, Quality of Water Branch

WRD Distribution: A, 8, S, FO, PO

Key words: water quality, equipment, field measurements, pH,
precipitation

This memorandum supersedes no previous memorandum.

This memorandum supplements Quality of Water Branch Technical
Memorandum 80.19.

[KDodds]

Cheers Paul. Just going by experience, notations of pH changes amongst dozens, if not hundreds of aquarists over the years and how simply cracking a window (or moving a skimmer air intake outside) can serve to raise pH. If atmospheric CO2 is 330ppm, and it doubled in a home to 660ppm, do you not think it might have an effect?

[pcsb23]

Cheers Paul. Just going by experience, notations of pH changes amongst dozens, if not hundreds of aquarists over the years and how simply cracking a window (or moving a skimmer air intake outside) can serve to raise pH. If atmospheric CO2 is 330ppm, and it doubled in a home to 660ppm, do you not think it might have an effect?
Not really, no. The tendency is for CO2 to leave the water, when the water is agitated the CO2 is driven off. Given that in the high tech planted tanks we are only looking at 30ppm CO2 and that is using CO2 directly diffused into the water. Any time we agitate the surface the CO2 levels drop. The solubility of CO2 in water is dependant on many things, including the atmospheric pressure, temperature of the water, ionic content of the water and the ph too. Add in organic and inorganic content and it gets more complicated.

Given that the fish give off CO2 too then there is always CO2 present in the water, lessening any tendency for more CO2 to dissolve in the water.

[Ronald]

Hi all,

Since you live in south FL it could have to do with the varios layers the ground water goes through. As I lived in Sunrise FL I had a some problems with the pH to. I can't remember exactly what layers there are but there is coral as a layer involved. As I used a R/O at the time with the water coming out with a conductivity at 20 it was fine. The pH was stable at 6.5 after I reconed it with calcium, seasalt and salt. and let it sit for 24 hrs.
Without the R/O it was just a hassel.

Regards,
Ronald

[KDodds]

A quick google search will bring up a number of links you might find informative. Try searching on: ambient atmospheric co2 ph aquarium

You should be able to bring up this link:
http://www.advancedaquarist.com/issues/may2002/chem.htm

The above link is an article by Randy Holmes-Farley, widely regarded as THE man in water chemistry. Warning, though, high science content.

[pcsb23]

Interesting read, rather re-enforces what I said. The tendency is for CO2 to off gas. I suppose if atmospheric pressure were to suddenly increase then the tendency would be for more CO2 but given the relatively minor changes in atmospheric pressure then this just won't happen. It is really not a function of how much CO2 is present in the air at all, more a function of pressure. There is no question that water with differing composition in respect of carbonates as well as ph can hold differing levels of CO2, but it will always tend toward equilibrium, which will in effect mean the CO2 will tend to leave the water. Think of it more like a fizzy drink left for a few hours, it soon goes flat.

I suppose thinking this through a bit. If the water were not to contain any CO2 then under those extremely rare conditions the water would take some CO2 from the atmosphere, again it would only take enough to get to equilibrium. Again if this water was then agitated the CO2 would be driven off again. The likelihood of water without CO2 in an aquarium setup is I would think extremely remote.

Permeate from an RO unit will be high in gas content because gas molecules are much smaller than the minerals the membrane removes.

[KDodds]

Actually, he states specifically that the formation of carbonic acid, which will effect pH is linked to atmospheric CO2. If this did not happen, all RO water, all of the time, with a TDS reading of 0ppm, would be a "perfect" pH of 7.0. But we know that this does not happen, even under ideal circumstances, due to atmospheric CO2, which tends to drive pH down slightly. The higher the concentration of atmospheric CO2, the more pH will be driven down.

[CraigG]

The pH of the RO water from the pet store I go to is 6.0 I get mine in Hoffman Estates, IL my friend gets his from Lombard, Il which is about 30 minutes away and it's the same.

From what I've read that is around what usual RO water is in my area not sure if it's different from state to state.

[kpotter2]

From what I have read online from site to site is that pH and TDS can very. I am on a well with PH around 7.8 tds around 350 most of the time.This verys with the season.It is winter in Iowa right now so with my Tec 100gpd membrane ph comes out around 7.3 ish and tds of 13 and with out a DI you will not be at 0ppm from what I have read. As long as you don't see a very large swing in your testing then Your Membrane is working. I think it all depends on how fast the water is forced to enter the membrane. I am no expert,but this is what I read about when I bought my R/o to see if it was working right. I now this that the 24gpd membrane that was in my R/O before my 100gpd one was reading around 6.0 Ph and 8tds. Just keep in mind there are alot of factors. So from reading online and asking around it looks as if your readings can be all over the place. But to keep it in all fareness PH of around 7.0 or tds of no higher then 20ppm then I think your getting your water you need.


Thanks

Kyle

[Daniella]

Mine come out pure with 0 gh and 0 kh and ph is off the chart for acidity. it is below 6.

Not a trace of mineral left since I have also DI at the end of my RO unit. Nothing but pure water left.




At what PH is your RO water. Mine comes out at around 7 ppm, but at a PH of around 7.6


Does that seem normal?

[Steve_Warner]

Hi all,
As a few have stated here, as well as the quote from Hanna, you cannot get an accurate reading with a common electronic pH meter in water with a purity of approx 70 Micromho( I always thought it was about 40 or less) conductance or down due to the relationship of the hydronium-hydroxide balance relationship. From what I understand in speaking with a Chemist friend of mine, In water that is quite pure, the equilibrium equation of these two molecules is constantly changing at a rapid pace, due to them constantly crashing into each other(it's called "The self-ionization of water" rule or something like that), and thus cannot be accurately electronically measured(with our hand-held pens) at any given instance(which is why there are so many varied range readings across the board). The addition of minute amounts of atmospheric CO2 are enough to sway the delicate balance and give it an ever so slightly acidic LSI and hold the pH at a level right around 6.8, as mentioned here by a previous poster. This is explained in one of the discus books we all have.....just can't remember the name of it off the top of my head right now. You can google hydronium/hydroxide balance and read about this on the net. I believe the titration method is a much better way to measure low Micromho water, if I remember correctly(going off long-ago memory, since I haven't had discus for a few years now...bummer!) HTH


Steve

[Don Trinko]

IMO; Summing up all the previous information I get the following:

1. For various reasons it is difficult to accuratly measure the ph of ro water.

2. Since you are going to mix something with a much higher chemical content with the ro water it realy doesn't mater what ph your test reads for the ro water.
All of this IMO; Don T.

[Chad Hughes]

I agree with Don here. Since I mix with tap water, I typically allow my membranes to actually degrade until they are producing RO water of 50 tds. Once that happens I replace the whole series of filters.

* Sediment Filter
* Carbon Block
* DI filter
* RO membrane X 2

It goes back to zero TDS (average Ph of 6.7) and the cycle starts all over.

Best wishes!