Tested pH with lab pH meter and it's 7.5!

[KonradTO]

Hi all,
This morning before lights went on I collected some water from my tank and tested pH in the lab with a lab-grade pH meter.
It says 7.5. I also tested the meter with some calibration solution and it seems about accurate (0.1 difference from the solution at pH 7.0).
With my Sera tests it was looking much more like 8 than 7.5 so I never checked.
This is the situation with my tank:

32.5 g, probably 25g water only.
Closed with lid. Many advised against it but the house is quite old and I don't want to get molds from increased humidity. Also the tank is not completely sealed, there is some space between the lid and the glass and the filter compartment is open. I will try to run the aeration test later this week because I do not have a pH probe at home so I must areate the water outside at work if I manage.
About 1/8th of the volume is occupied by macros
I have 3 fish (YWG, 6 line wrasse, bicolor blenny) and 2 crabs I am worried about (hermit and porcelain crab)
DkH was about 10 last week, I increased it from 8 to 10 using baking soda when I realized it dropped to 8dkh, probably because of macro.
At the moment I have also a cyano/dino outbreak.

How is this possible? I have so much macro in my DT, I should have them absorbing CO2 right?
What I could do in the immediate to increase pH without hurting my animals?
As soon as I found out I turned on the air scrubber in the tank (I use it from time to time in my DT to clean the water). Should I leave it on longer then? maybe all night?

 

[KonradTO]

Also, could be that this was always the ph of the tank? I had the hermit for almost 2 months now and he seems healthy. He changed shell few times and molted at least once

 

[KonradTO]

Bump (sorry for bumping but I am a bit worried for my crabs)

 

[Darren in Tacoma]

The macro algae is not going to consume an appreciable amount of co2. It will lower nitrates and phosphates though. Creating a good water/air interface will help to release the co2, thus increasing ph. What is it that you have referred to as an air scrubber?

 

[KonradTO]

The macro algae is not going to consume an appreciable amount of co2. It will lower nitrates and phosphates though. Creating a good water/air interface will help to release the co2, thus increasing ph. What is it that you have referred to as an air scrubber?

I basically flood the DT with microbubbles from the air pump

 

[Darren in Tacoma]

I'm guessing you don't have a sump?

I would try the aeration test before doing anything other than trying to increase gas exchange.

 

[Randy Holmes-Farley]

The macro algae is not going to consume an appreciable amount of co2. It will lower nitrates and phosphates though. Creating a good water/air interface will help to release the co2, thus increasing ph. What is it that you have referred to as an air scrubber?

Why would you say that macroalgae do not take up appreciable CO2? I certainly disagree.

I also disagree that tank top aeration will increase pH. In a home with elevated air CO2, it will lower pH.

A CO2 scrubber removes CO2 from the home air entering a skimmer intake.

 

[Randy Holmes-Farley]

I basically flood the DT with microbubbles from the air pump

Aeration with normal home air is not typically a solution to low pH. It often makes the problem worse.

 

[KonradTO]

Why would you say that macroalgae do not take up appreciable CO2? I certainly disagree.

I also disagree that tank top aeration will increase pH. In a home with elevated air CO2, it will lower pH.

A CO2 scrubber removes CO2 from the home air entering a skimmer intake.

What if I do not have a skimmer?

 

[ReefGeezer]

I would do a two point calibration of the meter (7.0 & 10.0) before I trusted its reading. Unless there is something acidic being added to the tank, a pH of 7.5 is hard to reach, particularly with decent alkalinity. Poor gas exchange could account for some lowering of the pH, not that much.

 

[Randy Holmes-Farley]

What if I do not have a skimmer?

There are lots of ways to raise pH, if you think you need to. Growing macroalgae, using carbonate or hydroxide (better) for alkalinity when you need alkalinity, more fresh air to the room, etc.

 

[Borat]

I would do a two point calibration of the meter (7.0 & 10.0) before I trusted its reading. Unless there is something acidic being added to the tank, a pH of 7.5 is hard to reach, particularly with decent alkalinity. Poor gas exchange could account for some lowering of the pH, not that much.

Two point calibration is not needed here.. Let's say that you calibrated to PH 7.0 but you are off on PH10 by 0.5 (i.e. you meter says PH10 instead of PH10.5 - which is a massive mis-calibration). Then your PH7.5 reading is only off by 0.08,i .e. it's actually PH7.58 instead of measured/shown PH7.5..

 

[Borat]

Try taking the tank cover off - wait for a day and measure PH again around the same time of the day. This will tell if your lack of exchange with open air is an issue. The second test to do is to increase turbulence of water surface by directing powerheads upwards and ensuring the pump return outlet is close to the surface. Again - implement it and see if PH improves (it may theoretically get worse as Randy said - if there is a lot of CO2 in the room)!


As Randy suggested - there are multiple ways to increase PH and my approach to it is "every little helps", i.e. usually no single way will solve all of your PH issues - but implementing a combination of them would help improve the PH..

 

[ReefGeezer]

Two point calibration is not needed here.. Let's say that you calibrated to PH 7.0 but you are off on PH10 by 0.5 (i.e. you meter says PH10 instead of PH10.5 - which is a massive mis-calibration). Then your PH7.5 reading is only off by 0.08,i .e. it's actually PH7.58 instead of measured/shown PH7.5..

I can't argue that I know better. I always thought that two-point calibration was needed and calibrate my probes that way. FWIW, if my meter reported a pH of 7.5 while my alkalinity was in the normal range, I would immediately suspect my probe.

I'd not quibble with the reading if it were 7.8 or possibly even 7.7. IMHO, high CO2 levels or poor gas exchange alone just can't explain a lower number in even a marginally operating system.

 

[Randy Holmes-Farley]

I would do a two point calibration, unless the meter does not allow it.

 

[Borat]

I can't argue that I know better. I always thought that two-point calibration was needed and calibrate my probes that way. FWIW, if my meter reported a pH of 7.5 while my alkalinity was in the normal range, I would immediately suspect my probe.

I'd not quibble with the reading if it were 7.8 or possibly even 7.7. IMHO, high CO2 levels or poor gas exchange alone just can't explain a lower number in even a marginally operating system.

My post was about explaining the implications of not doing 2 point calibration. If you want to measure PH of solution that is around 7.1 - and you calibrated your probe to PH7.0, would you still do a 2 point calibration? Of course you would get a more accurate result if you do (maybe by 0.001PH), but understanding (conceptually/mathematically) the implications of using or not using 2 point calibrations for me is more important than "I have done my 2 point calibration and I trust every number that comes out of it".

I have 4 PH probes in use and spent a lot of time thinking whether I should or should not recalibrate my probes frequently and how many/which calibration points are useful. All my probes are DIY controller controlled - so I can do as many point calibration as needed:
- for alkalinity test where the main point is PH4 I check that the probe accurately measure around that PH. Of course I would occasionally check 7.0 and I would definitely not be bothered about 10.0 calibration
- for CaRx with PH6.0 water (2 probes, one for each reactor chamber) I worry about both 4.0 and 7.0 calibrations as it's somewhere in the middle, again - not at all bothered about 10.0 calibration
- for tank water measurement I am worried mostly about 7.0 and 10.0. I don't care about 4.0 calibration in this instance..

 

[ReefGeezer]

...- for tank water measurement I am worried mostly about 7.0 and 10.0. I don't care about 4.0 calibration in this instance..

Yep... if measuring water in the tank, 7.0 & 10.0 are the standards to use. Like Randy said, "If the meter will allow it".

 

[Darren in Tacoma]

Why would you say that macroalgae do not take up appreciable CO2? I certainly disagree.

I also disagree that tank top aeration will increase pH. In a home with elevated air CO2, it will lower pH.

A CO2 scrubber removes CO2 from the home air entering a skimmer intake.

This was not a blanket statement that macro do not take up co2, but in this case. The op stated that they have a 32 gal display with about 25gal of water and 1/8 the volume of the tank filled with macro. They also stated that the ph was 7.5 with a calibrated probe. Doesn't sound to me like the macro is adjusting the ph a whole lot, although the test was taken in the morning after, I assume, the lights were out all night. I also suggested doing the aeration test because we don't know the co2 level in this persons home, do we?

 

[Randy Holmes-Farley]

would you still do a 2 point calibration?

I would, in ANY circumstance. The analysis you give assumes the pH 7 buffer is perfect. They can easily be off. using 2 or more buffers drops the chance (or extent) of being off due to an off buffer.

I tested a whole lot of calibration buffers for this article, and I found pH 7 buffers that I got both online and from an LFS to be as high as pH pH 7.5 and as low as pH 6.85.

http://reefkeeping.com/issues/2005-02/rhf/index.htm

 

[Borat]

I would, in ANY circumstance. The analysis you give assumes the pH 7 buffer is perfect. They can easily be off. using 2 or more buffers drops the chance (or extent) of being off due to an off buffer.

I tested a whole lot of calibration buffers for this article, and I found pH 7 buffers that I got both online and from an LFS to be as high as pH pH 7.5 and as low as pH 6.85.

http://reefkeeping.com/issues/2005-02/rhf/index.htm

If your buffer 7.0 is off by 0.5 and you do a 2 point calibration - this would not save your day.. In my example the 7.1 solution would read 7.6 with single point calibration and 7.58 with 2 point calibration - how is that helping you?

I think you are trying to signifity the importance of multiple reference solutions (of same PH standard) than about multiple point calibration. I would totally agree with this - it's more important to question the validity of your buffer reference solution than "I shall do a 2 point calibration irrespective".