Ph of rodi water

[trainbob]

My rodi water has a ph of 5.7 is this a problem or is it normal

 

[HankstankXXL750 Verified Sponsor]

What you really need to know is what is your pH of freshly mixed water. The salt mix will change the pH. If it mixes to what you want there is no problem. Otherwise you might need to change the pH after mixing either through aeration or buffers.

 

[HankstankXXL750 Verified Sponsor]

Here’s an article I found.
https://www.123filter.com/ac/why-reverse-osmosis-water-is-acidic

 

[trainbob]

Thanks for your reply and the article. Now I know why s advocate a remineralization filter

 

[Randy Holmes-Farley Verified Community Expert]

Thanks for your reply and the article. Now I know why s advocate a remineralization filte

I believe I have a much more accurate and useful answer to that question:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

Final Effluent pH

Aside from the issues discussed above concerning the effluent’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 aquarium’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 6’s and even into the 5’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 5’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 kit’s indicator dye is enough to alter pure water’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 pH’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).

 

[Jamie814]

I believe I have a much more accurate and useful answer to that question:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com

Final Effluent pH

Aside from the issues discussed above concerning the effluent’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 aquarium’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 6’s and even into the 5’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 5’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 kit’s indicator dye is enough to alter pure water’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 pH’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).

Great info, Thanks Randy!

 

[Randy Holmes-Farley Verified Community Expert]

Here’s an article I found.
https://www.123filter.com/ac/why-reverse-osmosis-water-is-acidic

That article is filled with bogus misinformation. I’d suggest not reposting it at REEF2REEF unless you believe it is accurate and want to debate the pseudoscience in it.

 

[TnFishwater98]

I have just realized this also. I’ve never tested PH on my top of water before. However my son got an African Dwarf Frog and I told him we needed to transfer it from a .5 gallon to a 5 gallon tank. I’ve never done freshwater tanks besides the classic goldfish in a bowl when I was a kid. So I used my RO/Di water to cycle the tank. Obviously when testing PH tested at the low end of the scale. So this was also new info to me. So questions is , having low 5-6 ph top-off water will not affect the tanks Ph correct? Even if top off sensor goes in idle mode for some reason and you have to add a lot of top off water to correct the salinity ?

 

[trainbob]

Thanks Randy your response is greatly appreciated and it is good to know that my top off water is not adversely affecting the ph of the tank.

 

[HankstankXXL750 Verified Sponsor]

That article is filled with bogus misinformation. I’d suggest not reposting it at REEF2REEF unless you believe it is accurate and want to debate the pseudoscience in it.

Thanks. I just did a quick look at the first part where it stated that pure water was 7 and RO/DI could quickly change to as low as 5 which is what the op was questioning. I should have read farther.
As you stated in a later post, the real factor is your pH post mix.
Thanks for the heads up.

 

[Randy Holmes-Farley Verified Community Expert]

having low 5-6 ph top-off water will not affect the tanks Ph correct? Even if top off sensor goes in idle mode for some reason and you have to add a lot of top off water to correct the salinity ?

That is correct. :)

 

[wrgoff]

I too noticed by testing my RODI water it was at 6.7. I was expecting it to be around 8. I had to do some reading as to why this is. So this leads me to my next question. For my Tank, almost every time I test it it sits at 7.8. Like clock work. I try to bring it up to 8.1 to 8.4 using Alkaline buffer (or some thing else). Should I even be concerned? The fish seem fine. I don't really have any corals (yet) just some zoas. Is this even something I should be chasing?

 

[Randy Holmes-Farley Verified Community Expert]

I too noticed by testing my RODI water it was at 6.7. I was expecting it to be around 8. I had to do some reading as to why this is. So this leads me to my next question. For my Tank, almost every time I test it it sits at 7.8. Like clock work. I try to bring it up to 8.1 to 8.4 using Alkaline buffer (or some thing else). Should I even be concerned? The fish seem fine. I don't really have any corals (yet) just some zoas. Is this even something I should be chasing?

Buffers always raise alkalinity, and alk will
often get too high without much pH boost.

There are many ways to raise pH if you want to, but they are not critical at pH 7.8.