Correlation with Temperature and pH

Mike and I were talking today about the graphs that our reef controllers display for temp and pH and the correlation that they share. It seems that every time the tanks temperature climbed, the pH would shortly follow suit, and of course when the temp drops so does the pH.

Why does this happen? Is it some type of reaction within the waters chemistry? If so what?

Or is that the nature of using a probe? Does it have something to do with the probe acting differently to varying temperatures that results in giving faulty readings?

Curious minds need to know...

I just looked at mine and it is interesting to see that is does.

Thinking about it even more... and I know I'm slow.....I know...

When my tank gets warmer it's because the lights are on, and when the lights are on photosynthesis is taking place in the corals which raises the pH....

Is that the reason why?

when photosynthesis happen the ph goes up and when the lights go out it goes down. My system has lights on for all most 14 hours total but 7 hours on one part of the system and then 7 hours on a different part of the system. For the real reason why this happened Paul might be able to explain or I could get DR Tim to give me an answer and I could post it hear. I am interested my self..

I just send an email to DR Tim to see what he has to say about this. I have learned a lot about water cem from him.

I've met him twice and have enjoyed our conversations. he certainly is a wealth of knowledge.

you got that right

Yes this is a good topic, maybe it can be presented at the next meeting. Btw, if you go to reeftronics and check other users data it matches the theory.

That's what got me thinking more about it.

Two things, one is your pH setting on the controller temp compensated? 2, as you said when your lights are on your corals are photosynthesizing and your tank is also heating up. Your pH and temp should both go up when the lights are on unless you are running a very tight temp control, like chiller and heater to hit one temp.

ok hears that makes the levels change.

Per Dr Tim.

It's all due to carbon dioxide (CO2)

Photosynthesis consumes CO2 (and produces O2) and less CO2 means the pH goes up

Once the lights go off and photosynthesis stops the process reverses and as more CO2 enters the water the pH drops


it is funny I knew thing because that is what happend in a cal reactor. you inject co2 to lower the ph in the reactor to break doew the media in the reactor.

shapermike wrote:ok hears that makes the levels change.

Per Dr Tim.

It's all due to carbon dioxide (CO2)

Photosynthesis consumes CO2 (and produces O2) and less CO2 means the pH goes up

Once the lights go off and photosynthesis stops the process reverses and as more CO2 enters the water the pH drops


it is funny I knew thing because that is what happend in a cal reactor. you inject co2 to lower the ph in the reactor to break doew the media in the reactor.

That is exactly what both Jimmy and I were saying. What isnt addressed is Temp which is a variable that can be controlled to eliminate the temp spike if you want. You will still see the pH spike though. You can try to reduce the size of the spike with a refugium running at night, but it doesnt work too well. Your refugium would have to be huge. Even with all my tanks running at different times, I still see a spike in pH in the evenings when my biggest tank lights come on.

I agree. It is interesting how every little thing can cause an effect on the parameters. Love this hobby… you learn some much and when you think you understand there is something new that comes up….