True or false? PH in top off RO water is irrelevant and will not change PH in tank

[MissMolly]

Hi, so I have decided to buy a kitchen top RO device like Aquadrop for both me and topping off the tank. (Long story short: I'm not able to get a under the sink system but everyone advises me to use RO water for top off - I use AF Perfect Water for WC).

Obviously concerned about PH and then researched... Came across a discussion in a thread on another community where one stated that:

"Pure water will always have a pH somewhere around 7, depending on dissolved gas levels. This is because it entirely lacks buffering chemicals like alkalinity. None of those buffers evaporate, so using it as top off will have no impact on tank pH. Salt mix has lots of buffers, so it makes no difference there either. As long as your RO/DI is pure, the pH is irrelevant."

IS THIS TRUE?! Please educate a lost soul!!!

BR, Line Evelin

 

[Garf]

Hi, so I have decided to buy a kitchen top RO device like Aquadrop for both me and topping off the tank. (Long story short: I'm not able to get a under the sink system but everyone advises me to use RO water for top off - I use AF Perfect Water for WC).

Obviously concerned about PH and then researched... Came across a discussion in a thread on another community where one stated that:

"Pure water will always have a pH somewhere around 7, depending on dissolved gas levels. This is because it entirely lacks buffering chemicals like alkalinity. None of those buffers evaporate, so using it as top off will have no impact on tank pH. Salt mix has lots of buffers, so it makes no difference there either. As long as your RO/DI is pure, the pH is irrelevant."

IS THIS TRUE?! Please educate a lost soul!!!

BR, Line Evelin

Sort of yes. However adding RODI to saltwater will temporarily increase pH a little, don't know why, but it does, lol

 

[Randy Holmes-Farley]

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

from it:
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).

 

[MissMolly]

Sort of yes. However adding RODI to saltwater will temporarily increase pH a little, don't know why, but it does, lol

Thank you for the answer! I guess I should have paid more attention in school

 

[MissMolly]

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

from it:
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).

Thank you Randy. I read this but I still don't understand it. Like I just can't comprehend But maybe that is okay. As long as you can confirm with me that it's safe to just top off with RO water without adding anything, right?

I have just picked up the RO device from Waterdrop and according to my reasearch it should make very, very clean water.

 

[Randy Holmes-Farley]

0-1 ppm tds water is always suitable regardless of what a pH meter might read in it.

 

[MissMolly]

0-1 ppm tds water is always suitable regardless of what a pH meter might read in it.

THANK you Randy, I don't know what I would do without your help (and ohers in here on this forum of course)

 

[Randy Holmes-Farley]

You're welcome.

Happy Reefing.

 

[bratfink]

interesting discussion. I was trying to figure out why my probe was reading 9.3 in my ATO. Great info, thanks.

 

[Randy Holmes-Farley]

Glad it was useful. Happy Reefing!