Another Low pH Thread

[deuce6371]

I have done the searches and I am tired of reading the same causes and fixes over and over. :headwally: Let me summarize where I am at right now.

1. Parameters such as Alk, Ca and Mg out of balance - These are and have been in balance for at least the last 4 months. I had a spike in Alk prior to that, which caused a decrease in Ca and Mg but it was corrected. Now it is steady at Alk = 9.5, Ca = 440 and Mg = 1350.

2. CO2 buildup for sources such as a closed up house or Calcium reactor effluent. - I have brought in a CO2 meter from work (lab grade and calibrated and found I have 0.0% CO2 and over 19% O2, I went ahead and installed an extra skimmer which is setup to pull outside air in. The Ca reactor is functioning properly and has a secondary chamber that is also reciculating and drips in the filter sock as an added measure to get CO2 dispersal.

3. pH probe is not calibrated. - recalibrated with new fluids from work. Took sample into work and ran them on two different pH meters. Both gave me the same results as the pH meter at home.

4. Dose a form of hydroxide (calcium/sodium). Since my Ca is where I wanted it I chose to think outside the box and try NaOH. It did bring the pH up but only temporarily. I would have to have a steady drip on it to keep it where I wanted it. This could be an option, any comments??

5. Have refugium on a reverse cycle. Did this no change.

6. Extra water changes. Been doing 20% weekly or more. No change.

7. Don't worry about pH. I don't buy this. I keep having coral bleaching and colors are horrid!

Is there any other root causes/fixes I am missing? Is there someone out there battling the same thing. I am assuming there is an acid production somewhere either CO2 based or maybe some other biological function but I am out of ideas.

Thanks, John

 

[disc1]

2. If you found 0.0% CO2 then your measurement had to be wrong. You should see at least normal atmospheric levels. What type of instrument did you use?

4. Dosing hydroxide is dosing alkalinity. If you put that on a continuous drip you're just going to end up pushing alkalinity through the roof. And the pH will come right back down to equilibrium like you've already seen with this.

7. Maybe pH is a symptom and not a cause? Maybe it is a clue to what is really bleaching your corals.

 

[deuce6371]

2. If you found 0.0% CO2 then your measurement had to be wrong. You should see at least normal atmospheric levels. What type of instrument did you use?


4. Dosing hydroxide is dosing alkalinity. If you put that on a continuous drip you're just going to end up pushing alkalinity through the roof. And the pH will come right back down to equilibrium like you've already seen with this.

7. Maybe pH is a symptom and not a cause? Maybe it is a clue to what is really bleaching your corals.

2. Sorry correction it was 0.02 left of the last digit. The unit I used was a Bacharach infra red CO2/O2 monitor. It was just calibrated by an outside source to applicable standards and is used to monitor incubator concentrations for microorganism growth. It also goes through a internal check.

4. Will dosing NaOH raise alkalinity? Not sure I understand the chemistry behind that could you please explain,

7. thats what I am trying to find out. :headwalls:

 

[billsreef]

Have you tried vigorously aerating a sample and rechecking pH?

BTW, considering atmospheric CO2 is approximately 400ppm, and oceanic acidification is being seen at that level, I don't think a CO2 meter that reads in percent will give you readings worth even bothering with.

 

[disc1]

You haven't said yet. How low is the pH?

How does the CO2 meter read? Is it in ppm or % or partial pressure? If the monitor is for measuring the concentrations in incubators, then it might not be very applicable for atmospheric levels. Depends on the meter.

If I'm looking at the right meter, it has 0-20% range for CO2 with 0.1% increment? The atmospheric concentration of CO2 is 0.03%. So you might not be able to see the changes responsible for a pH issue with that resolution. Can you link to the monitor you used?


Yes, NaOH will increase alkalinity. You're adding base aren't you? Each OH- ion is one equivalent of alkalinity. There's nothing in the world that you can add that would raise pH and not raise alkalinity at the same time. That's a simple part of the definition of alkalinity. If you are adding more basic equivalents then the alkalinity (defined as number of basic equivalents) is going up.

Technically, with hydroxide you aren't adding carbonate equivalents so there are a number of vendors who try to claim that it doesn't affect carbonate alkalinity. In reality seawater is strongly buffered with carbonate being the main buffer by orders of magnitude. Any addition of hydroxide results in some carbonic acid (CO2 + H2O) being converted to bicarbonate resulting in a net increase in carbonate alkalinity. The carbonic acid gets replaced by ambient CO2 in short order and the pH drops back down but the increase in carbonate alkalinity remains.

This is the same reason we use kalk (calcium hydroxide) to increase both calcium and alkalinity in a fixed balanced ratio. The alkalinity comes from the hydroxide ions in the kalk. It reacts with CO2 to give bicarbonate.

The real problem that you run into chasing pH with sodium hydroxide or buffers is that as the alkalinity climbs the water is more and more heavily buffered. This means it takes more and more hydroxide every time to shift the pH up by the same amount, which raises the alkalinity even faster... eventually it turns into a runaway situation which usually ends in a snowstorm of calcium precipitation.

 

[billsreef]

NaOH dosing is done in aquaculture in some instances. Though it's generally a last resort sort of thing in heavily stocked systems, due to both the expense and issues David mentioned.

 

[deuce6371]

7.8 at night 7.95 during the day.

Good points all. I have not considered several of the CO2 meter points. I think you may be right the resolution is only 0.1%. I think I was way wrong in my memory of the reading. It was about a month ago. Now that I think about it was 0 bouncing to 0.1. That could make much more sense. Makes me wonder where I got 0.02 at now.

The alkalinity discussion makes sense thanks for the explanation.

I have not tried aerating the sample yet but I will.

 

[billsreef]

For good measure, aerate the sample outside. A pH of 7.8 is low enough to be a problem. BTW only a mere 50ppm increase in atmospheric CO2 has impacted seawater pH sufficiently to cause observable negative impacts in experiments looking at the issue of ocean acidification. So it doesn't real take much.

 

[azjohnny]

IMO 7.8-8.0 isn't bad. High ALK will cause bleaching


Are you carbon dosing? That can cause lower PH levels