High alkalinity but low pH

[AllSignsPointToFish]

My alkalinity has been running 11.5-12.3, but my pH has been hovering around 8.0. The alkalinity is high because I've been dosing more of Randy's carbonate/bicarbonate recipe, but the pH just won't respond.

In the past, increasing the dosage seemed to work better. I don't use kalkwasser regularly, and I attempted to calibrate my pH probe last night, but I need more calibration fluid (which is ordered and on the way).

I performed a water change on Saturday, but the situation has been going on for the last week or so even before the water change.

Any thoughts on what could cause pH to be lower than expected when the dKh is so high?

 

[AllSignsPointToFish]

Oh, and I checked the pH with my API test kit as a backup, and it showed 8.1-8.2.

I'm guessing this is a pH probe issue?

 

[Downbeach]

There's nothing wrong with a pH of 8, and is very common. I successfully ran a 180 mixed reef for many years with a pH between 7.8 and 8.1. As long as your alk is within acceptable ranges, the issue is with the amount of CO2 in your system and the surrounding atmosphere. So, I wouldn't add any more supplement, pH boosters, etc. Here is a good article worth reading:

http://reefkeeping.com/issues/2004-09/rhf/index.php

 

[AllSignsPointToFish]

Thanks. I'm not sure I buy the whole CO2 hypothesis as I don't have any natural gas appliances in my household. Also, I was able to maintain a higher pH 2-3 weeks back with lower alkalinity, which is why I suspect a shift in the pH probe. Unless the CO2 situation is strongly influenced by the number of people in the household, I can't see why my house would have elevated CO2 levels. I actually ran a line to the exterior to the house for fresh air intake for my skimmer as a test and found no change in pH after running that way for more than two weeks.

Unfortunately, I'm going out of town next week for 8 days, and this has me rattled. I will soak the pH probe in vinegar tonight and recalibrate after rinsing with RO/DI water.

 

[Downbeach]

There are a number of things that can produce CO2, including the number of people in the house, i.e. more people = more respiration = elevated CO2 = lower pH through the gas exchange in your system.

Another read here:

http://www.advancedaquarist.com/2004/2/chemistry

 

[Randy Holmes-Farley Verified Community Expert]

Thanks. I'm not sure I buy the whole CO2 hypothesis as I don't have any natural gas appliances in my household. Also, I was able to maintain a higher pH 2-3 weeks back with lower alkalinity, which is why I suspect a shift in the pH probe. Unless the CO2 situation is strongly influenced by the number of people in the household, I can't see why my house would have elevated CO2 levels. I actually ran a line to the exterior to the house for fresh air intake for my skimmer as a test and found no change in pH after running that way for more than two weeks.

Unfortunately, I'm going out of town next week for 8 days, and this has me rattled. I will soak the pH probe in vinegar tonight and recalibrate after rinsing with RO/DI water.

Again pH 8.0 is fine and quite normal for the elevated CO2 levels many people have in homes. It is more common than not. Don't worry about this pH.

pH being low due to Co2 is not a hypothesis, unless the pH measurement is off, but you can test it easily enough with an aeration test described in the above articles. pH is determined mathematically by the CO2 level in the water and the alkalinity.

 

[AllSignsPointToFish]

Again pH 8.0 is fine and quite normal for the elevated CO2 levels many people have in homes. It is more common than not. Don't worry about this pH.

pH being low due to Co2 is not a hypothesis, unless the pH measurement is off, but you can test it easily enough with an aeration test described in the above articles. pH is determined mathematically by the CO2 level in the water and the alkalinity.

Thank you, Randy and Downbeach. I should've been more specific...what I meant to say is that I'm not convinced the high CO2 in my household is causing the low pH. However, the diurnal pH swing often bottoms out at around 7.9 then would rebound to 8.1-8.2 during the day. I was having some issues over the last couple of weeks before my two house guests arrived, so I'm not sure hypothesizing that elevated ambient CO2 levels inside the house holds any validity.

The part that has me really confused is that my Apex pH probe is only three months old, so a shift in the pH measurement over such a short time with new equipment is worrisome.

I have tried to use limewater to raise pH, but the effect seems to be temporary unless I convert to a constant dosing system.

 

[jason2459]

Have you cleaned the probe off at all in the past 3 months? Soft toothbrush could work. Otherwise vinegar quick and toothbrush. Or just needs re-calibrated. 3 months isn't unheard of.

 

[AllSignsPointToFish]

Have you cleaned the probe off at all in the past 3 months? Soft toothbrush could work. Otherwise vinegar quick and toothbrush. Or just needs re-calibrated. 3 months isn't unheard of.

I have not cleaned it. I was planning on doing that tonight before I recalibrated

 

[Randy Holmes-Farley Verified Community Expert]

Thank you, Randy and Downbeach. I should've been more specific...what I meant to say is that I'm not convinced the high CO2 in my household is causing the low pH. However, the diurnal pH swing often bottoms out at around 7.9 then would rebound to 8.1-8.2 during the day. I was having some issues over the last couple of weeks before my two house guests arrived, so I'm not sure hypothesizing that elevated ambient CO2 levels inside the house holds any validity.

The part that has me really confused is that my Apex pH probe is only three months old, so a shift in the pH measurement over such a short time with new equipment is worrisome.

I have tried to use limewater to raise pH, but the effect seems to be temporary unless I convert to a constant dosing system.

I expect it is elevated CO2 in the home air, but if not, more aeration will bring up the pH (assuming it is accurate).

 

[AllSignsPointToFish]

I have an 8" Reef Octopus skimmer on a 125 gallon tank that runs continuously. Lol. I'm not sure I could anymore aeration

 

[Randy Holmes-Farley Verified Community Expert]

I have an 8" Reef Octopus skimmer on a 125 gallon tank that runs continuously. Lol. I'm not sure I could anymore aeration

But with perfect aeration, there is no daily swing in pH (assuming steady alkalinity and no changes in the home air). People misunderstand how hard it is to equilibrate CO2. Much harder than O2.

 

[AllSignsPointToFish]

Interesting. I appreciate the input. At my work, we remove CO2 from groundwater with a large fan that exchanges oxygen for carbon dioxide. I have recalibrated the pH probe three times this evening with new solution, and all three times it showed the same result. I've added some limewater to bring the pH up to a little over 8, and I added an air stone and air pump to the sump. Still no dice. Guess I will have to try aerating a sample of tank water outside, but I don't really have a portable pH meter (my only pH meter is attached to the Apex).

Apologies for being so hardheaded, Randy. I really appreciate you always being there to help out!

 

[Randy Holmes-Farley Verified Community Expert]

Interesting. I appreciate the input. At my work, we remove CO2 from groundwater with a large fan that exchanges oxygen for carbon dioxide. I have recalibrated the pH probe three times this evening with new solution, and all three times it showed the same result. I've added some limewater to bring the pH up to a little over 8, and I added an air stone and air pump to the sump. Still no dice. Guess I will have to try aerating a sample of tank water outside, but I don't really have a portable pH meter (my only pH meter is attached to the Apex).

Apologies for being so hardheaded, Randy. I really appreciate you always being there to help out!

Your work system doesn't exchange carbon dioxide for oxygen, but it certainly can exchange both at the same time. The exchange of each is independent of the other. But CO2 is rather slow to hydrate and dehydrate from carbon acid to CO2 that can leave the water. It can take many seconds for these processes, so CO2 does not rapidly exchange. Because it is so slow, animals have enzymes to speed the process so they can exhale CO2 more quickly.

 

[AllSignsPointToFish]

Well, that's news to me since the well water we use in our process needs to be stripped of CO2 before being added to the process or else big corrosion problems occur

This system has been around for a while, so I'm pretty sure it works. However, it is designed to strip CO2 out of groundwater. I must also add that the local groundwater has excess CO2 in it beyond the level that would be expected for normal atmospheric equilibrium concentrations, which is probably why the system works

 

[Randy Holmes-Farley Verified Community Expert]

Degassing definitely works, I was just clarifying details about how it works.

 

[AllSignsPointToFish]

Fair enough!

 

[Downbeach]

Well, that's news to me since the well water we use in our process needs to be stripped of CO2 before being added to the process or else big corrosion problems occur

This system has been around for a while, so I'm pretty sure it works. However, it is designed to strip CO2 out of groundwater. I must also add that the local groundwater has excess CO2 in it beyond the level that would be expected for normal atmospheric equilibrium concentrations, which is probably why the system works

Although the process is different, the affect will be the same. Blowing air past running water with a fan, will allow the CO2 contained in the water to reach equilibrium with the surrounding atmosphere. Blowing air through water in your system, using an air stone, skimmer/venturi, etc. will allow the CO2 in that water to reach equilibrium with your households surrounding atmosphere. So, the less CO2 in the house, the higher the pH will be, conversely the higher the CO2 in the house the lower the pH will be, once equilibrium has been reached. So, if you can bring in air with a lower concentration, by opening windows, etc., allowing more air with a lower concentration into the house will allow your pH to increase.

 

[AllSignsPointToFish]

Unfortunately, opening a window in Florida during the summertime isn't really an option

 

[AllSignsPointToFish]

I will be participating in an unplanned test next week. We will be out of the house for several days, so there should be no CO2 generators in the house. If high ambient CO2 is the cause of the low pH, I would expect to see some improvement next week. Guess we'll see!