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

3.8K views 23 replies 8 participants last post by  TUCCI  
#1 ·
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?
 
#2 ·
I've not heard of the pH being different in 2 identically set up tanks that have different temperatures so this would be a first for me. My first guess would be not cleaning the test tube thoroughly between tanks or after the last time the pH tester was used though your later tests on established tanks may make that thought moot.
 
#5 ·
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 is now lower), 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.
 
#12 ·
Ahhhh yes.... the Nitrate thing.
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.
And Reverse Osmosis filtration?
DON'T DO IT.
Trust me on this, that RO trail will take you DEEP into that 'Briar Patch'. And, if I could do it again? I would have definitely avoided the RO filtration I resorted to in stripping the mineral hardness out of the water to soften/acidify it enough for those sensitive WC Geophagines to be happy. Keep it simple - enjoy success!
So, to get the Nitrates under control in your systems I like what you are doing in utilizing those Pothos to hoover them out of the water for you. To boost up those Nitrate reducing effects, you may ultimately wind up going with a dedicated plant refugium for one (or more) of those tanks.
 
#6 ·
That situation is pretty odd. At a measured 7.0 and below PH out of the tap, your water is different anyway from a lot of municipal water sources these days. Since Flint Michigan, the tap water everywhere has been getting more additives in it to boost the PH and hardness.
Is your tap water also pretty soft/low in KH and GH values? Without much to buffer your water, those changing PH levels can happen a lot more easily.
 
#10 ·
That situation is pretty odd. At a measured 7.0 and below PH out of the tap, your water is different anyway from a lot of municipal water sources these days. Since Flint Michigan, the tap water everywhere has been getting more additives in it to boost the PH and hardness.
Is your tap water also pretty soft/low in KH and GH values? Without much to buffer your water, those changing PH levels can happen a lot more easily.
Normally my tap water is: pH 7.6, gH 9 degrees kH 3 degrees. So kH is a little low. Tap water never tested positive for nitrates before today but it is not unusual for a city water supply to fluctuate a little. Aware that a low kH can contribute to pH swings. All my established tanks are stable: pH 7.2 ish, nitrite 0 ammonia 0, nitrate always 20-40 ppm. Who knows. I'm thinking if my city water nitrate levels hover @ 5ppm I should not need to RO and then put mineral additives for tank replacement water.

Do you use Seachem Prime declorinator? Prime is known to affect ammonia readings. I haven’t heard about it affecting PH readings but it may be possible?
Yes I use Prime. Have never seen any literature that shows it to affect pH. My understanding is that high ammonia levels can acidify water especially if the kH is low.
 
#9 ·
Normally my tap water is: pH 7.6, gH 9 degrees kH 3 degrees. So kH is a little low. Tap water never tested positive for nitrates before today but it is not unusual for a city water supply to fluctuate a little. Aware that a low kH can contribute to pH swings. All my established tanks are stable: pH 7.2 ish, nitrite 0 ammonia 0, nitrate always 20-40 ppm. Who knows. I'm thinking if my city water nitrate levels hover @ 5ppm I should not need to RO and then put mineral additives for tank replacement water.
 
#14 ·
Well I learned something new yesterday. A gentleman on another site gave me a little chemistry lesson
"The nitrifying bacteria destroy 7.14 mg of CaC03 alkalinity per 1mg of ammoniam Ion oxidised,. Alkalinity is what keeps the ph stable, but the neutralisation of the hydrogen Ions produced during the nitrification process reduces the CaC03. This in turn is what has reduced your pH (insufficient alkalinity CaC03)".

Now I know that the nitrification process will all but stall at ph of 6 resulting in a rise in ammonia.
Therefore, I believe the addition of a ph buffer (I used Seachem Alkalinity Buffer 1 tsp in each 40 gallon tank) will add the needed alkalinity to return my tanks to their desired ph level to kick start the nitrification process again. We'll see when I test the water later today.🤞
 
#18 ·
The short answer is yes. Temperature can effect pH and do so dramatically. There's a little over 100 years of research on this.

If you ever go crazy or get really bored and have a sensitive enough testing device you can literally chart swings in pH based on a variety of factors. Temperature is one of the easy ones. The higher your temperature the easier it is for water to ionise and the lower your pH will drop. This is of course an oversimplification but you get the idea. Before LED lights became as popular as they are now you could usually see a swing in pH depending on if your lights were on or off due to the high heat generated.

In point of fact, from a scientific perspective a pH measurement WITHOUT an accompanying temperature is totally useless.
 
#19 ·
So - Yes. A different temperature can lead to different pH readings, but it does not change the actual pH or the ability to bind hydrogen within the solution...
It appears that, since your tanks are not 200 degrees F apart from each other, that the predictable temp differential would be minimal.
How Does Temperature Affect pH? Westlab.

Image



In my opinion, though, you've already put your finger on it. Please forgive me if you've said it here, can you tell us the nitrates actually in the tanks?

I'm actually guessing that fishless cycling increased nitrates too much which caused the pH crash and a cycle stall. The whole thing stops when you're aggressively trying to cycle a tank and the nitrogen starts to build. I've done this. To see if I'm correct, you can tell us the nitrate number, then do a full water change on both systems, and then see where they go. I'm not sure how much ammonia you'd already put in, but 1ppm Ammonia dosed this way will turn into about 18ppm Nitrates once it's been processed.
 
#22 ·
So - Yes. A different temperature can lead to different pH readings, but it does not change the actual pH or the ability to bind hydrogen within the solution...
It appears that, since your tanks are not 200 degrees F apart from each other, that the predictable temp differential would be minimal.
How Does Temperature Affect pH? Westlab.

View attachment 142352


In my opinion, though, you've already put your finger on it. Please forgive me if you've said it here, can you tell us the nitrates actually in the tanks?

I'm actually guessing that fishless cycling increased nitrates too much which caused the pH crash and a cycle stall. The whole thing stops when you're aggressively trying to cycle a tank and the nitrogen starts to build. I've done this. To see if I'm correct, you can tell us the nitrate number, then do a full water change on both systems, and then see where they go. I'm not sure how much ammonia you'd already put in, but 1ppm Ammonia dosed this way will turn into about 18ppm Nitrates once it's been processed.
I had initially determined nitrates were between 40-80ppm when it crashed. In the meantime I did learn a new trick with the API test kits on how to get better readings. As we all know that API color chart is a nightmare until I learned this little bit of info. For instance the API color chart between 40 & 80 ppm for nitrate is almost identical to me. However one trick to differentiate between those 2 values is if after the drops are placed in the tube and it is shook look at the color. If it's orangish and then turns reddish later during that 5 minute wait time interval the reading is closer to or 40ppm. If it's reddish right out of the gate it will be closer to the 80 ppm. You can also use this differentiation for their nitrite test. So in retrospect I believe the nitrate reading was closer to 40ppm based on my results.
 
#20 · (Edited)
Like I said it's all REALLY over-simplified, especially on nitrates causing a pH crash. Nitrates causing a pH crash is kind of a funny subject in my community. If you'd like to debate a few Ph.D. and candidates on this the University of Georgia biology and marine biology department will talk your freakin' ear off. :LOL: No joke, things get heated with the academic types too, wow is all I have to say...

Last I checked they've settled on nitrates don't cause a pH crash, how you are filtering or moving water while having high nitrates is causing the crash or some such riggamaroll.

Suffice to say that unless all your variables are the lab-grade exact same in your tanks it's pretty easy to achieve different results. The testing equipment you are using is "Meh" on its best day and the methodology involved is <insert massive shrug here>. Really as long as you can achieve stable measurements near the range that's desirable you're fine. If you're not sure how to get it there then continue to make small adjustments using the tried and true methods, measuring always in the most consistent way you can achieve.

EDIT: I'm serious about if you want to talk these guys really seem to love chatting about the subject of aquatic animals. Colleges are a great source of information. They've saved my reef tank from utter destruction at least twice. E-mail or even call your local marine biology or freshwater science department. They will likely appreciate it and also be very nice about it.
 
#21 ·
They've saved my reef tank from utter destruction at least twice.
I just HAVE to share...they helped me figure out my neighbor was accidentally killing my reef tank. I live in a condo. He had incorrectly installed a clothes dryer on the opposite side of the wall from where my reef tank was embedded. Heat from the dryer was roasting my reef tank whenever he turned it on. It was a long journey to figure that out and holy **** I was very surprised.
 
#23 · (Edited)
Interesting read. Im no chemist or biologist but I have been keeping fish for a few years and have seen some strange things do strange things to tank chemistry. I think the first thing to estabilish is that in general, our hobbyist grade water test kits SUCK. They are OK from a repeatability stand point but from an accuracy standpoint, they are not that good. I used to be obsessed with testing my reef tank until I relized that keeping the value constant was far more important than the actual value (as long as you are within "normal" parameters etc).

Take for example the beloved API test kit. Most people assume that when the manufacturer states fill with 5ml of water to the mark on the test vial, the line will be accurate. Over the years I've had vials with lines that have been +- 1.5ml. On a 5ml test. Thats a huge! I ignore the line and use a syringe.

Then there are simple "environmental" factors that can effect tank chemistry. The classic example I used to encounter was dropping ph during the winter because I had all my windows closed and a well insulated house. The answer was as simple as cracking the window in my fish room and installing a ceiling exhaust fan to help improve fresh air intake for my skimmer. In addition I put my refugium on a opposite light cycle from my display.

So, while it might seem a little odd to have 2 tanks that use the same water source have different parameters, its probably a) not that unusual considering the test kits we use and b) highly likely that any number of local environmental factors effect each tank different within the same building.

What I've learned is to let my tanks and the inhabitants be the determining factor. I get a tank's chemistry in the rough area, watch the inhabitants and make adjustments accordingly. Most of the time, just keeping parameters stable is good enough.
 
#24 ·
Interesting, my tap water is .25 NH3s with 0.0 on N02s & N03s before I even put it in my tank. When I lived in Arizona, their tap water was .25 NH3s also. I’ve truly never seen 0.0 on any municipal NH3 readings. (Using API liquid test kits that are not expired). What’s up with that ?