Why does pH rise and fall with temperature changes?

[calvertbill]

i got an APEX controller after i saw it at MACNA and since it logs temp,. pH and ORP readings i've noticed that the tank's pH is directly proportional to it's temperature.

The answer will probably embarrass me because i feel like i should know it but...

WHY?

 

[kurt_n]

My guess is that you don't have the "temperature compensation" option enabled on the pH probe setup page. I'm not a chemist, but I don't believe pH changes (measurably) with minor changes in temperature.

 

[JSimpson]

I think it's actually that both the temp and ph are proportional to your lighting. Lights come on, temps start rising, ph starts rising. Lights off and both will tend to drop.

 

[Allmost]

correct.

PH is a function of atmospheric pressure or altitude, CO2 level, Carbonates [alkalinity], Salinity, and Temp.


Kurt ... temp compensation if for reading the salinity.

lighting ... when on, PH rises ... even if temp stays constant ... this is due to growth of algae [or photosynthesis in general], O2 VS CO2 concentration in water [as algae takes it up]

HTH,

 

[thabizness]

I just checked my Apex. There is a Temperature compensation on/off setting there. I have read it will change with temp but very little.

 

[disc1]

Temp has a direct effect on pH, but in the narrow range of temps we keep in our fish tanks it doesn't much matter. The effect you are seeing on your apex is most likely due to the fact that both are reacting to the lights.

 

[kurt_n]

...Kurt ... temp compensation if for reading the salinity. ...,

Yes, it's there for conductivity (salinity) as well. But it is also available for pH.

Enabling or disabling it won't really make much of a difference for our tanks, as disc1 mentioned. But then, I'm not sure of how much change in pH the original poster is talking about. If we're talking about big changes, then yeah... that' just the normal lighting cycle.

 

[Allmost]

calculator for Equilibrium PH. can be found below :
http://www.hamzasreef.com/Contents/Calculators/EquilibriumPh.php

I should add, for more info ... change in temp, does change the response time (sensitivity) of the electrodes of the PH probe, so there might be some errors that can occur when temp changes .... but the True value of PH also changes with temp.

 

[kurt_n]

No... I'm not missing the point.

I stated that there was temperature compensation available for the pH probe on an Apex.

I took your direct reply to me to mean that I was mistaken, that temp compensation was for the salinity probe and not pH.

My response was to point out that temp compensation *is* available on the pH probe.

I think if you play with that calculator your posted, using normal reef temperatures, you'll find that pH really doesn't change any meaningful amount, say for temps between 75 and 80 degree F. A hundredth of a point in pH swing is nothing.

Regardless... temp compensation is available for the Apex pH probe - how you use it is up to you.

[Edit: Wow! That was quite an "edit" to your original post! Reads entirely different now! That'll teach me not to quote posts when reponding! :beer:]

 

[slief]

Temp has a direct effect on pH, but in the narrow range of temps we keep in our fish tanks it doesn't much matter. The effect you are seeing on your apex is most likely due to the fact that both are reacting to the lights.

+1. That was exactly my thoughts too. PH down at night and up during the daylight hours which would typically follow the temp swings as well.

 

[Allmost]

No... I'm not missing the point.

I stated that there was temperature compensation available for the pH probe on an Apex.

I took your direct reply to me to mean that I was mistaken, that temp compensation was for the salinity probe and not pH.

My response was to point out that temp compensation *is* available on the pH probe.

I think if you play with that calculator your posted, using normal reef temperatures, you'll find that pH really doesn't change any meaningful amount, say for temps between 75 and 80 degree F. A hundredth of a point in pH swing is nothing.

Regardless... temp compensation is available for the Apex pH probe - how you use it is up to you.

[Edit: Wow! That was quite an "edit" to your original post! Reads entirely different now! That'll teach me not to quote posts when reponding! :beer:]

I really dont feel like teaching today. you are taking the info way too personal ...

maybe David does ...

I gave u link to the calculator, u can use to find your error ... or not, either way ... and pointed out some facts. its up to the reader on how to use it ....

lol