huckilt
Community Member
I checked the ph of my ro/di water and it’s around 5.23. I was wondering what I could use to raise the ph closer to 8.0-8.3 so I don’t have a drop when adding fresh ro/di water to compensate for evaporation.
Ph in ro evap water
- Thread starter huckilt
- Start date
- Tagged users None
gbroadbridge
2500 Club Member
RO water has no buffering so it's pH can be anything.
As soon as it hits the tank it will have no effect.
As soon as it hits the tank it will have no effect.
gbroadbridge
2500 Club Member
Assuming a pH meter, if the pH probe is being stored in 3M HCl storage solution, residual from the probe will be pulling the ph down towards the measured level. It's inconsequential.
HuduVudu
2500 Club Member
First off why would you store a probe this way, and second why wouldn't you rinse the probe. Also you have no idea what volume of water is being measured, so there is no way to make assumptions about dilution.
You have made a lot of assumptions about what is taking place here. I really don't think that that is warranted. Better to ask questions of the OP and to clear up confusion than to give advice that might be detrimental.
piranhaman00
5000 Club Member
- Joined
- Jun 24, 2019
- Messages
- 5,023
- Reaction score
- 4,995
Pure water has pH of 7 but as soon as it’ equalizes with air it becomes 5.2 approx. so you are right on! No problem
Randy Holmes-Farley
Reef Chemist
Staff member
Super Moderator
Excellence Award
Expert Contributor
Article Contributor
R2R Research
My Tank Thread
There are several reasons to not measure the pH in RO/DI water at 0 ppm TDS . I show them below. But if it is not 0 ppm TDS, the pH of RO/DI water can range very widely. If either of the anion or cation beads in the DI deplete before the other, and the other is still working, the pH can be VERY high or low as the TDS rises. Far higher or lower than the incoming source water.
As to the actual pH of pure fresh water and what it means:
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 will not even result in a pH below 8.2, but rather will be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).
As to the actual pH of pure fresh water and what it means:
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 will not even result in a pH below 8.2, but rather will be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).
Malcontent
Valuable Member
- Joined
- Sep 20, 2018
- Messages
- 1,225
- Reaction score
- 1,200
You wouldn't believe how many people think they can test the calibration of a pH meter with distilled water. One Youtuber even said pH meters don't work because he got results that didn't make sense in distilled water.
