Test pH of RO/DI.

[Rook]

Randy.

Recently I've read some people recommend that when you mix fresh saltwater using RO/DI and your favorite brand of salt, that you should first aerate the RO/DI water for 12+ hours to driveoff any excess CO2 and equalize the pH of the RO/DI; then "remineralize" the RO/DI water with a alklinity buffer for 6-12+ hours; then go ahead and mix the salt in and aerate that for 24+ hours.

First, what's your take on that? Is this really necessary? The reasons stated where that to not do so resulted in trying to add salt to a low pH and unstable RO/DI will result in salt water with low pH and low alklinity levels and will shock the tank inhabitants.

It was also noted to "remineralize" the RO/DI water before using it for top-offs. What is your take on that?

Next, is it possible to measure the pH of RO/DI water accurately with a Pinpoint probe or pH test kit?

And, last what is a "tri-buffer" when talking about alklinity buffers?

Thanks :rollface:

 

[Randy Holmes-Farley]

The pH of RO/DI water has no significant impact on the pH of the salt mix. Aerating RO/DI can only bring in CO2 and lower the pH. CO2 will not make it through the DI.

Here are my comments on it:

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

from it:

Final Effluent pH

Aside from the issues discussed above concerning the effluentââ"šÂ¬Ã¢"žÂ¢s pH when the DI resin becomes depleted, the final pH coming out of an RO/DI system should not significantly concern reef aquarists. Many aquarists with low pH problems have asked, for example, if their aquariumââ"šÂ¬Ã¢"žÂ¢s low pH may be caused by their replacing evaporated water with RO/DI water that they measure to have a pH below 7. In short, the answer is no, this is not a cause of low pH nor is it something to be generally concerned about, for the following reasons:

1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6ââ"šÂ¬Ã¢"žÂ¢s and even into the 5ââ"šÂ¬Ã¢"žÂ¢s, depending on the amount of CO2. At saturation with the level of CO2 in normal (outside) air, the pH would be about 5.66. Indoor air often has even more CO2, and the pH can drop a bit lower, into the 5ââ"šÂ¬Ã¢"žÂ¢s. Consequently, the pH of highly purified water coming from an RO/DI unit is expected to be in the pH 5-7 range.

2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kitââ"šÂ¬Ã¢"žÂ¢s indicator dye is enough to alter pure waterââ"šÂ¬Ã¢"žÂ¢s measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.

3. The pH of the combination of two solutions does not necessarily reflect the average (not even a weighted average) of their two pH values. The final pH of a mixture may actually not even be between the pHââ"šÂ¬Ã¢"žÂ¢s of the two solutions when combined. Consequently, adding pH 7 pure water to pH 8.2 seawater may not even result in a pH below 8.2, but rather might be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).

 

[Rook]

Thanks for the quick reply

So, in a nut shell, for top-off, the pH of RO water is not a concern. I also then assume it is not a concern for mixing salt. Thus, mixing salt in regular RO water is perfectly fine. Of course you need to buffer the new salt water for calcium and alklinity and mix it good for 24 hours or so...

What about using RO water for fresh water dips, whether for fish or corals? You typically would want the temperature and pH of the RO water to be near that of the salt water, right? I then assume you could buffer RO water with baking soda and aerate it, which would then allow you to measure the pH with a probe or test kit??

 

[Randy Holmes-Farley]

So, in a nut shell, for top-off, the pH of RO water is not a concern. I also then assume it is not a concern for mixing salt. Thus, mixing salt in regular RO water is perfectly fine

:thumbsup:

Yes.


Of course you need to buffer the new salt water for calcium and alklinity and mix it good for 24 hours or so...

If it is deficient in some way, yes.

What about using RO water for fresh water dips, whether for fish or corals?

Some people do add a pinch of baking soda, at least when doing long term hyposalinity treatments. For a dip, I can't see how the pH matters too much, and I wouldn't adjust it, but you could add a pinch of baking soda there too. I'd use a meter, but a kit might work fine.

 

[Rook]

Thanks again for all the help

 

[GTR]

Re: Test pH of RO/DI.

<a href=showthread.php?s=&postid=6530264#post6530264 target=_blank>Originally posted</a> by Rook




And, last what is a "tri-buffer" when talking about alklinity buffers?

Unless I just missed it... I was wondering myself.

SteveU

 

[Habib]

Meant probably Tris (TrisH/Tris) Buffer

 

[GTR]

Habib... I don't get it (but I'm sure you are not surprised).

What's "Tris (TrisH/Tris) Buffer"? A brand?

SteveU

 

[Rook]

I think the person who used the term ment it as a mix of three buffers as opposed to a "mono" buffer like baking soda.

 

[Randy Holmes-Farley]

Tris is an organic buffer used to hold pH in the region around 8 or so. It would not be added to a reef aquarium, but could be added to a seawater solution where one wanted to keep a shipping bag from dropping too much in pH as CO2 is released from the organism. I would not add it to a fresh water dip.

 

[Habib]

Remember that for next years reef chemistry quiz.

 

[pk1]

Randy, I think this is where Rook got the idea on the RO/DI PH and new saltwater, from a discussion over at Anthony Calfo's new home that is currently being held.

http://www.marinedepot.com/FORUMS/Topic21343-13-1.aspx

Quote From Anthony

"the gist of the demineralized water issue is rather short and sweet. RO/DI water is neutral to acidic and very unstable (crashed to low pH easily). For you to get it to saltwater useful condition... it must be buffered op to an average mineral hardness. If you do not, then adding it raw to your system is a huge burden on your ALK, CA, etc as they are reduced (ameliorated really) by the demineralized what that is coming in. A bad dilution.
Yet so much of it can be avoided. Aerating raw RO or DI water offgasses nitric acid that is lowering the RO water pH. Then adding back good minerals to buffer the demineralized water will be less of a burden on display water when they are averaged.

Using raw RO or DI water is a common cause for flow ALk or Ca in aquaria.

--

Regarding freshly deminderalized water: Pending the quality of your DI resin and/or RO membrane and subsequent purity of product water, you will note that typically the raw, demineralized water is indeed very low in pH. Even when it is not acidic (rare) it is something close to neutral at best. And even in the rarest(!) cases when their is any alkaline lean to its pH... the water is categorically unstable, as defined by its lack of buffering (ALK) minerals - principally carbonate hardness.

Aerating such "weak" (buffer/ALK) water drives off carbonic acid which is temporarily depressing the pH of such demineralized product water.

So what that does is gives you a water, albeit unstable, with a higher starting pH before adding seabuffer/baking soda and/or sea salt. Thus... less of the added buffers are "neutralized" to get the raw demineralized water to the target measure of pH and/or Alkalinity you want."

So in reading this, do you think aerating is beneficial for the overall makeup of new saltwater? If it is, maybe this helps explain some aquarists' low Calcium readings on fresh synthetic seawater? For example, I have 40 gallons of RO/DI made up in a closed container for a few weeks, do I -- toss in the required amount of salt and mix for a water change(my usual method)....or aerate first for X amount of time then add salt?

Patrick

 

[Randy Holmes-Farley]

Well, I disagree with Anthony on the pH effect.

It is certainly true that if one uses tap water with calcium and alkalinity in it (or RO/DI water with those things added to it), the resulting water will have more calcium and alkalinity in it.

But salt mixes vary all over the map with respect to calcium and alkalinity. Some have excessive calcium (like Oceanic), some have high alkalinity (like IO). There is no general need for both of these. If your salt mix needs one of the other (or maybe both), then by all means add what is necessary to the new salt water (or the tank, when needed). I add calcium and magnesium to my IO.

Aerating RO/DI water will only lower the pH (and may or may not add O2). Aerating after the salt is added will bring the pH into line with the alkalinity and CO2 level in the air.