Does temperature affect pH readings. This one has me baffled.

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aussieman57

aussieman57

Aimara
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Nov 11, 2021
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I am in the process of cycling two new 40 breeder tanks. They are set up EXACTLY the same: pool filter sand (same bag), two sponge filters. Placed heaters in yesterday & ran overnight (have not adjusted temp yet).
Tested the water today:
Tank 1: pH 6.0 (completely yellow) Temp is 84 degrees
Tank 2: pH 7.4 Temp is 80 degrees

My first thought was my pH test kit was no good. However, I tested established tanks & all pH readings come out at 7.4
Test kit is API Master Freshwater Kit with expiration in 2026 & is @ 4 months old and has worked flawlessly. What the heck is going on here?
 
This pH shift is not surprising.
Water from the tap (under pressure in the pipes) may be saturated with gases until they disassociate when put in a tank, a filter runs, and water sits in the tank over night, and if the gases are high in CO 2, pH will rise as they off gas, and the tank reaches normal equilibrium.
 
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duanes said:
This pH shift is not surprising.
Water from the tap (under pressure in the pipes) may be saturated with gases until they disassociate when put in a tank, a filter runs, and water sits in the tank over night, and if the gases are high in CO 2, pH will rise as they off gas, and the tank reaches normal equilibrium.
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Agree with above. The only problem here is that these tanks have had water in them running with sponge filters for over a week. The only thing that changed is I placed heaters in 2 days ago, let them sit in tanks for 24 hours and then plugged them in last night. Reading my initial post I can see that it is confusing and looks like everything was set up 24 hours ago. I thoroughly cleaned test tubes & re-ran these tests 3 times. Bizarre. I may bring a water sample to LFS and see what they get. I've never run into this before.
 
Temperature actually really affects ph tests. But the difference is in the second digit after the dot. Which means that it doesnt matter much in the hobby. I think in your case it is like duanes said.
 
You nay also want to consider that the cooler the water, the more dissolved gases water can hold (if those gases are CO2), lower pH.
As water warms over time, those trapped gases are released, pH rises.
Water at 50'F can be super saturated, water at 80'F holds much less, not only CO2, but also oxygen.
When we'd do pH testing in the lab, samples were not allowed to sit open for any length of time, indoors, because pH could then "not" be considered accurate.
 
I did a little interweb search and see that temp can influence pH by @ .2 like Milingu states. But this difference is @ 1.6 so most likely not this.
And I agree warmer water does not have the ability to hold gas as well as cooler water. Why fish seek cooler water in summer months for more oxygen.
The problem here is that the warmer tank is the one with the lower pH which is the exact opposite of what it's ability to hold onto C02 (which lowers pH) should be. So as I sit here now questioning my sanity I'm still baffled. My tap water pH is 7.6
So, I just re-tested both tanks and now they both read in the yellow. Also re-tested both established tanks and they come back at pH 7.4.
Shouldn't heating the tanks cause C02 to off gas resulting in a higher more alkaline state. Why the drop in pH?
 
Actually warmer water holds less gas in general. 02, CO2, etc etc
When I worked as a chemist in drinking water treatment treatment plant, i would see pH shifts of over 1.0, even up to 1.5 pH shifts over time, as water warmed, and aged, and not just 10ths.
There are many other factors that come into play, that may influence pH, not just one.
Substrate, aeration, filtration , if your water is treated with chlorine, and the time it takes for the chlorine to off gas, are just a few.
Another also had to do with alkalinity.
Highly alkaline water can hold pH stable much longer than low alkaline water, no matter the temp.
 
"And I agree warmer water does not have the ability to hold gas as well as cooler water."
" Actually warmer water holds less gas in general. 02, CO2, etc etc "
We are both saying the same thing only in different ways.
City water here is treated with chloramine. When I initially set up the tanks I dosed them with SeaChem Prime. Per the wife the tanks have been up and running for over 2 weeks (I thought over 1 week but trust her memory better).
Took water sample to LFS and pH also tested at 6.0 so my test kit is working.
Here is what I think may have happened. I am doing a fishless cycle using ammonia (Fritzyme Fishless Fuel). I believe for some reason the nitrification cycle stalled ??? as ammonia level is now @ 2ppm , nitrite 0 , nitrate between 40-80ppm.
3 days ago ammonia was 0.50 ppm nitrite 0.25 ppm (did not test nitrate) pH 7.4 For whatever reason I believe the system crashed causing ???an acidification from ammonia increase???. Anyway I am going to use some alkaline buffer to bring the pH back up to where the nitrification process will re-establish it's progress (as this process is retarded by this acid pH). Hopefully this will get this moving in the right direction again.
Tested my city tap water again today pH 7.0 (not sure why it tests lower now), ammonia 0, nitrite 0, nitrate 5ppm. Not crazy about the nitrate in my city water but wonder if it is low enough to avoid having to start using an RO system to produce water. Explains why I can never seem to get my tank water below 20 ppm nitrate.
Interesting turn of events if nothing else.
 
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