pH - Diurnal variations in my tank

[JulesH]

Hi,

I have been dosing Kalk for about two months now. I had some pH measurement issues with my two probes but now I have settled on one particular probe, which calibrates well.

Now I have stopped dosing Kalk for the last two weeks as I have noticed my pH creeping up. I now get a diurnal peak of 8.65 and a low of 8.28 overnight without adding anything. The tank inhabitants don't show any signs of stress.

Should I be concerned?

 

[arking_mark]

Those numbers are probably +/-0.2 accuracy. So probably fine.

 

[JulesH]

Thats interesting thanks Mark. I been trying to find out the accuracy of the Neptune pH probe. Perhaps I am not looking hard enough?

 

[arking_mark]

Let's say you're use a high-alk salt, perfect indoor air quality, and perfect tank aeration...expect pH is 8.38 NBS.

 

[arking_mark]

Neptune at best is +/- 0.1...more likely closer to +/- 0.2.

 

[JulesH]

Thanks Mark, what is 'NBS' after pH please, what software are you using?

 

[arking_mark]

NBS is what most people use for pH
...National Bureau of Standards.

PyCO2Sys is the python library.

 

[JulesH]

Thank you Mark.

 

[Randy Holmes-Farley Verified Community Expert]

I expect that pH of 8.65 is not accurate when not dosing kalkwasser, unless the alkalinity is very high.

If it is that high, simple aeration will lower it.

 

[JulesH]

I expect that pH of 8.65 is not accurate when not dosing kalkwasser, unless the alkalinity is very high.

If it is that high, simple aeration will lower it.

Hi Randy, can I ask why you say the pH is not accurate when not dosing kalwasser, my alkalinity is 9.3.

 

[gbroadbridge]

Hi,

I have been dosing Kalk for about two months now. I had some pH measurement issues with my two probes but now I have settled on one particular probe, which calibrates well.

Now I have stopped dosing Kalk for the last two weeks as I have noticed my pH creeping up. I now get a diurnal peak of 8.65 and a low of 8.28 overnight without adding anything. The tank inhabitants don't show any signs of stress.

Should I be concerned?

I don't believe the pH of 8.65 is accurate.

Which buffers did you use to calibrate your probe?
Were they freshly opened (high pH buffers go bad pretty fast).

 

[Randy Holmes-Farley Verified Community Expert]

Hi Randy, can I ask why you say the pH is not accurate when not dosing kalwasser, my alkalinity is 9.3.

I base that on thousands of reported values for pH from reef tanks, and when no high pH additives are in significant use, and alk is not unusually high, pH that high ends up being testing error.

It's hard to get pH that high. Without high pH alk additives, it requires a lot of photosynthesis and not very much aeration.

Normal reef tanks have plenty of aeration to keep photosynthesis from driving pH that high.

 

[JulesH]

My buffers are from a company called APC in the UK. they specialise in lab consumables. the buffers are about 1 month old.

 

[JulesH]

I base that on thousands of reported values for pH from reef tanks, and when no high pH additives are in significant use, and alk is not unusually high, pH that high ends up being testing error.

It's hard to get pH that high. Without high pH alk additives, it requires a lot of photosynthesis and not very much aeration.

Normal reef tanks have plenty of aeration to keep photosynthesis from driving pH that high.

OK, thanks for that.

 

[JulesH]

Randy, looking at my last reply, I certainly wasn't questioning your judgement and apologies if it seems that way. The issue was with me I did not understand your answer.

 

[gbroadbridge]

My buffers are from a company called APC in the UK. they specialise in lab consumables. the buffers are about 1 month old.

Did you calibrate using ph 7.01 and 10.01?

 

[JulesH]

Indeed I did sir.

 

[Randy Holmes-Farley Verified Community Expert]

Randy, looking at my last reply, I certainly wasn't questioning your judgement and apologies if it seems that way. The issue was with me I did not understand your answer.

I didn't take it that way, and it is ALWAYS appropriate to question things that do not make sense or that do not give a convincing rationale.

 

[JulesH]

As I understand the chemistry of Calcium hydroxide, the raising of pH stops soon as you stop doing or very nearly so?

 

[David_CO]

When I'm out of town for work for longer then 3-4 days my indoor CO2 reports at 380-400ppm. My PH seems to cap out at 8.55 with pretty heavy kalk dosing. It reliably gets to that exact point and flatlines trip after trip (using a neptune PH probe). During this time my diurnal swing goes down to ~8.35ish